Selector device for two-terminal memory

ABSTRACT

Solid-state memory having a non-linear current-voltage (I-V) response is provided. By way of example, the solid-state memory can be a selector device. The selector device can be formed in series with a non-volatile memory device via a monolithic fabrication process. Further, the selector device can provide a substantially non-linear I-V response suitable to mitigate leakage current for the non-volatile memory device. In various disclosed embodiments, the series combination of the selector device and the non-volatile memory device can serve as one of a set of memory cells in a 1-transistor, many-resistor resistive memory cell array.

CROSS REFERENCE TO RELATED APPLICATIONS

This application for patent claims the benefit of U.S. provisionalpatent application Ser. No. 61/951,454, entitled SELECTOR DEVICE FOR TWOTERMINAL DEVICE and filed Mar. 11, 2014, and claims the benefit of USprovisional patent application Ser. No. 62/021,660, entitled FASTApplications and filed Jul. 7, 2014, each of which are incorporated byreference herein in their respective entireties and for all purposes.

TECHNICAL FIELD

This disclosure relates generally to electronic memory, for example, thedisclosure describes a selector device configured to provide non-linearcurrent-voltage response for a memory device.

BACKGROUND

A recent innovation within the field of integrated circuit technology isresistive memory. While much of resistive memory technology is in thedevelopment stage, various technological concepts for resistive memoryhave been demonstrated by the assignee of the present invention and arein one or more stages of verification to prove or disprove associatedtheory(ies). Even so, resistive memory technology promises to holdsubstantial advantages over competing technologies in the semiconductorelectronics industry.

Resistive random access memory (RRAM) is one example of resistivememory. The inventors of the present disclosure believe RRAM has thepotential to be a high density non-volatile information storagetechnology. Generally, RRAM stores information by controllably switchingamong distinct resistive states. A single resistive memory can store asingle bit of information, or multiple bits, and can be configured as aone-time programmable cell, or a programmable and erasable device, asvarious memory models demonstrated by the assignee provide.

Various theories have been proposed by the inventors to explain thephenomenon of resistive switching. In one such theory, resistiveswitching is a result of formation of a conductive structure within anotherwise electrically insulating medium. The conductive structure couldbe formed from ions, atoms that can be ionized under appropriatecircumstances (e.g., a suitable electric field), or other chargecarrying mechanisms. In other such theories, field-assisted diffusion ofatoms can occur in response to a suitable electric potential applied toa resistive memory cell. In still other theories proposed by theinventors, formation of the conductive filament can occur in response tojoule heating and electrochemical processes in binary oxides (e.g., NiO,TiO₂, or the like), or by a redox process for ionic conductors includingoxides, chalcogenides, polymers, and so on.

The inventors expect resistive devices based on an electrode, insulator,electrode model to exhibit good endurance and life cycle. Further, theinventors expect such devices to have high on-chip densities.Accordingly, resistive elements may be viable alternatives tometal-oxide semiconductor (MOS) transistors employed for digitalinformation storage. The inventors of the subject patent application,for instance, believe that models of resistive-switching memory devicesprovide some potential technical advantages over non-volatile Flash MOSdevices.

In light of the above, the inventors endeavor to make furtherimprovements in memory technology, and resistive memory.

SUMMARY

The following presents a simplified summary of the specification inorder to provide a basic understanding of some aspects of thespecification. This summary is not an extensive overview of thespecification. It is intended to neither identify key or criticalelements of the specification nor delineate the scope of any particularembodiments of the specification, or any scope of the claims. Itspurpose is to present some concepts of the specification in a simplifiedform as a prelude to the more detailed description that is presented inthis disclosure.

In various embodiments of the present disclosure, there is provided aselector device for solid state memory applications. The selector devicecan be configured to have a non-linear current-voltage (I-V)relationship, in various embodiments. Furthermore, the selector devicecan, in isolation, be a volatile device that has a first electricalstate in response to a first electrical condition, and a secondelectrical state in absence of the first electrical condition.

In one or more embodiments, disclosed is a monolithic solid stateconstruct formed in series with a non-volatile memory device. Themonolithic solid state construct can be a selector device, as providedherein. Further, the selector device can provide a substantiallynon-linear I-V response suitable to mitigate leakage current for thenon-volatile memory device. Thus, in at least some embodiments, theseries combination of the monolithic solid state construct and thenon-volatile memory device can serve as one of a set of memory cells ina 1-transistor, many-resistor (1T-nR) resistive memory cell array (e.g.,the memory cell being a 1-selector, 1-resistor (1S-1R) configuration).

In still additional embodiments, disclosed is a selector deviceconfigured to exhibit a non-linear I-V relationship to differentpolarity signals. For instance, the selector device can exhibit a firstnon-linear I-V relationship in response to a signal of a first polarity,and a second non-linear I-V relationship in response to a second signalof a second polarity. In some embodiments, the first non-linear I-Vrelationship and the second non-linear I-V relationship can have similaror the same curvatures, whereas in other embodiments the firstnon-linear I-V relationship and the second non-linear I-V relationshipcan have different curvatures. The selector device can be provided inseries with a bipolar memory device, in further embodiments. In suchembodiments, the selector device can provide a non-linear response forread and write operations of a first polarity, as well as eraseoperations of a second polarity.

In a further embodiment, there is provided a method for forming aselector device for a two-terminal memory device. The method cancomprise providing a first layer structure comprising a first metalmaterial and providing a layer of selector material in contact with thefirst layer structure. Moreover, the method can comprise providing asecond layer structure comprising a second metal material and in contactwith the layer of the selector material. In various embodiments, thefirst metal material or the second metal material can be configured toprovide conductive ions to the selector material in response to avoltage of a first polarity or a second polarity, respectively, appliedacross the first layer structure and the second layer structure and theselector material is configured to allow the conductive ions to permeatewithin the layer of selector material in response to the voltage appliedacross the first layer structure and the second layer structure. Inalternative or additional embodiments, the first layer structure, thelayer of selector material, and the second layer structure form theselector device and the selector device is disposed in electrical serieswith the two-terminal memory device.

In yet other disclosed embodiments, the subject disclosure provides aselector device for a two-terminal memory. The selector device cancomprise a first layer structure comprising a first metal material and alayer of selector material in contact with the first layer structure.Further, the selector device can comprise a second layer structure incontact with the layer of the selector material and comprising a secondmetal material. In some embodiments, the first metal material or thesecond metal material can be configured to provide conductive ions tothe selector material in response to a threshold voltage of a firstpolarity or a second polarity, respectively, applied across the firstlayer structure and the second layer structure. In other embodiments,the selector material is configured to allow the conductive ions topermeate within the layer of selector material in response to thethreshold voltage applied across the first layer structure and thesecond layer structure. According to still other embodiments, theselector device is disposed in electrical series with the two-terminalmemory device.

Further to the above, the disclosure provides a method of operating acrossbar memory array comprising a plurality of two-terminal memorydevices and a plurality of selector devices, wherein each of theplurality of two-terminal memory devices is associated in series withone selector device from the plurality of selector devices, wherein eachselector device is associated with a first electrical characteristic inresponse to an applied voltage less than a threshold voltage, andassociated with a second electrical characteristic in response to anapplied voltage greater or equal to the threshold voltage. The methodcan comprise applying a first voltage greater than the threshold voltageto a first memory structure comprising a first two terminal memorydevice in series with a first selector device. The method canadditionally comprise applying a second voltage, concurrently withapplying the first voltage, that is less than the threshold voltage to asecond memory structure comprising a second two-terminal memory devicein series with a second selector device. Moreover, the method cancomprise determining a current in response to applying the first voltageconcurrent with applying the second voltage. In at least one embodiment,the current comprises a first current associated with the first selectordevice and a second current associated with the second selector device.In one or more additional embodiments, a current ratio of the firstcurrent to the second current is within a range of ratios selected froma group of ranges consisting of: about 1,000 to about 10,000, about 10,000 to about 100,000, about 100,000 to about 1,000,000, and about1,000,000 to about 10,000,000. In light of the present disclosure,current ratios in excess of 10,000,000 are envisioned.

The following description and the drawings set forth certainillustrative aspects of the specification. These aspects are indicative,however, of but a few of the various ways in which the principles of thespecification may be employed. Other advantages and novel features ofthe specification will become apparent from the following detaileddescription of the specification when considered in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects or features of this disclosure are described withreference to the drawings, wherein like reference numerals are used torefer to like elements throughout. In this specification, numerousspecific details are set forth in order to provide a thoroughunderstanding of this disclosure. It should be understood, however, thatcertain aspects of the subject disclosure may be practiced without thesespecific details, or with other methods, components, materials, etc. Inother instances, well-known structures and devices are shown in blockdiagram form to facilitate describing the subject disclosure;

FIG. 1 depicts a block diagram of an example monolithic structureproviding a solid state selector device according to various disclosedembodiments;

FIG. 2 illustrates a block diagram of a sample selector device behaviorin response to an electrical characteristic of a first polarity;

FIG. 3 depicts a block diagram of a sample selector device behavior inresponse to an electrical characteristic of a second polarity;

FIG. 4 illustrates a block diagram of a sample selector device accordingto alternative or additional aspects of the present disclosure;

FIG. 5 depicts a diagram of an example current-voltage (I-V) response ofa selector device, in some embodiments;

FIG. 6 depicts a diagram of a sample I-V response of a selector devicein other disclosed embodiments;

FIG. 7 depicts a block diagram of an example selector device provided inconjunction with a memory device, according to an embodiment(s);

FIG. 8 illustrates a block diagram of an example arrangement of memorycells comprising respective selector devices in series with two-terminalmemory;

FIG. 9 depicts a diagram of a sample crossbar memory architectureillustrating effects of leakage current and benefit of non-linear I-Vresponse;

FIG. 10 illustrates a flowchart of a sample method for fabricating aselector device, according to various disclosed embodiments;

FIG. 11 depicts a flowchart of an example method for fabricating a solidstate selector device in series with a two-terminal memory device;

FIG. 12 illustrates a flowchart of an example method for operating anarray of memory cells according to further disclosed embodiments;

FIG. 13 depicts a block diagram of a sample operating and controlenvironment for a memory device according to various disclosedembodiments;

FIG. 14 illustrates a block diagram of an example computing environmentthat can be implemented in conjunction with various embodiments.

DETAILED DESCRIPTION

This disclosure relates to a selector device for a two-terminal memorycell employed for digital information storage. In some embodiments, thetwo-terminal memory cells can include a resistive technology, such as aresistive-switching two-terminal memory cell. Resistive-switchingtwo-terminal memory cells (also referred to as resistive-switchingmemory cells or resistive-switching memory), as utilized herein,comprise circuit components having conductive contacts with an activeregion between the two conductive contacts. The active region of thetwo-terminal memory device, in the context of resistive-switchingmemory, exhibits a plurality of stable or semi-stable resistive states,each resistive state having a distinct electrical resistance. Moreover,respective ones of the plurality of states can be formed or activated inresponse to a suitable electrical signal applied at the two conductivecontacts. The suitable electrical signal can be a voltage value, acurrent value, a voltage or current polarity, or the like, or a suitablecombination thereof. Examples of a resistive switching two-terminalmemory device, though not exhaustive, can include a resistive randomaccess memory (RRAM), a phase change RAM (PCRAM) and a magnetic RAM(MRAM).

Embodiments of the subject disclosure can provide a volatile selectordevice that can be integrated with a non-volatile memory cell. Invarious embodiments, the volatile selector device or the non-volatilememory cell can be filamentary-based devices. One example of afilamentary-based device can comprise: a conductive layer, e.g., metal,doped p-type (or n-type) silicon (Si) bearing layer (e.g., p-type orn-type polysilicon, p-type or n-type polycrystalline SiGe, etc.), aresistive switching layer (RSL) and an active metal layer capable ofbeing ionized. Under suitable conditions, the active metal layer canprovide filament forming ions to the RSL. In such embodiments, aconductive filament (e.g., formed by the ions) can facilitate electricalconductivity through at least a subset of the RSL, and a resistance ofthe filament-based device can be determined by a tunneling resistancebetween the filament and the conductive layer.

In various embodiments of a memory cell of the present disclosure, ap-type or n-type Si bearing layer can include a p-type or n-typepolysilicon, p-type or n-type polycrystalline SiGe, or the like. A RSL(which can also be referred to in the art as a resistive switching media(RSM)) can comprise, e.g., an undoped amorphous Si layer, asemiconductor layer having intrinsic characteristics, a Si sub-oxide(e.g., SiOx wherein x has a value between 0.1 and 2), and so forth.Other examples of materials suitable for the RSL could includeSi_(X)Ge_(Y)O_(Z) (where X, Y and Z are respective suitable positivenumbers), a silicon oxide (e.g., SiO_(N), where N is a suitable positivenumber), amorphous Si (a-Si), amorphous SiGe (a-SiGe), TaO_(B) (where Bis a suitable positive number), HfO_(C) (where C is a suitable positivenumber), TiO_(D) (where D is a suitable number), Al₂O_(E) (where E is asuitable positive number) and so forth, or a suitable combinationthereof. In various embodiments, the RSL includes a number of materialvoids or defects.

An active metal layer for a filamentary-based memory cell can include,among others: silver (Ag), gold (Au), titanium (Ti), titanium-nitride(TiN) or other suitable compounds of titanium, nickel (Ni), copper (Cu),aluminum (Al), chromium (Cr), tantalum(Ta), iron (Fe), manganese (Mn),tungsten (W), vanadium (V), cobalt (Co), platinum (Pt), hafnium (Hf),and palladium (Pd). Other suitable conductive materials, as well ascompounds, alloys, or combinations of the foregoing or similar materialscan be employed for the active metal layer in some aspects of thesubject disclosure. Some details pertaining to embodiments of thesubject disclosure similar to the foregoing example(s) can be found inthe following U.S. patent applications that are licensed to the assigneeof the present application for patent: application Ser. No. 11/875,541filed Oct. 19, 2007 and application Ser. No. 12/575,921 filed Oct. 8,2009, each of which are incorporated by reference herein in theirrespective entireties and for all purposes.

In various disclosed embodiments, filamentary-based switching devicesare disclosed and their operation is described. In some embodiments, afilamentary-based switching device can be a volatile switching device,which exhibits a first measurably distinct state in the absence of asuitable external stimulus, and exhibits a second measurably distinctstate in response to the suitable external stimulus. The volatilefilamentary-based switching device is often referred to herein as aselector device, or selection device, filamentary selector device,filamentary-based selector device, and so on; though such devices, theircomposition or application should not be limited by this terminology. Inother embodiments, a filamentary-based switching device can be anon-volatile switching device, which exhibits a first measurablydistinct state until a suitable first external stimulus is applied tochange the non-volatile switching device to a second measurably distinctstate. The non-volatile switching device then exhibits the secondmeasurably distinct state until a suitable second external stimulus isapplied. Non-volatile filamentary-based switching devices can have morethan two measurably distinct states, leading to multi-level cellfunctionality, though this disclosure refers generally to the binarycase. Non-volatile filamentary-based switching devices are generallyreferred herein as a memory cell, resistive memory cell,filamentary-based memory cell, or the like, but again the composition,function or application of such devices should not be limited by thisterminology.

A filamentary selector device can exhibit a first state (e.g., a firstelectrical resistance, or other suitable measurable characteristic) inthe absence of a suitable external stimulus. The stimulus can have athreshold value or range of such values that induces the filamentaryselector device to change from the first state to a second state whilethe stimulus is applied. In response to the stimulus falling below thethreshold value (or threshold range of values) the filamentary selectordevice returns to the first state. In some disclosed embodiments, afilamentary based selector device can operate in a bipolar fashion,behaving differently in response to different polarity (or direction,energy flow, energy source orientation, etc.) external stimuli. As anillustrative example, in response to a first polarity stimulus exceedinga first threshold voltage (or set of voltages), the filamentary selectordevice can change to the second state from the first state. Moreover, inresponse to a second polarity stimulus exceeding a second thresholdvoltage(s), the filamentary selector device can change to a third statefrom the first state. In some embodiments, the third state can besubstantially the same as the first state, having the same or similarmeasurably distinct characteristic (e.g., electrical conductivity, andso forth), having the same or similar magnitude of threshold stimulus(though of opposite polarity or direction), or the like. In otherembodiments, the third state can be distinct from the second state,either in terms of the measurable characteristic (e.g., differentelectrically conductivity value in response to the reverse polarity ascompared to the forward polarity) or in terms of threshold stimulusassociated with transitioning out of the first state (e.g., a differentmagnitude of positive voltage required to transition to the secondstate, compared to a magnitude of negative voltage required totransition to the third state).

In some embodiments, and by way of example, a disclosed filamentarybased selector device can form a conductive path or filament through arelatively high resistive portion in response to a suitable externalstimulus. The external stimulus can cause metallic particles within anactive metal layer to migrate within (or ionize within) a RSL layer ofthe filamentary selector device. Further, the RSL can be selected tohave relatively few physical defect locations for the volatilefilamentary switching device, facilitating relatively good mobility ofthe metallic particles within the RSL. Accordingly, below an associatedthreshold stimulus (or narrow range of threshold values), the metallicparticles can be dispersed within the RSL to prevent formation of asufficient conductive path through the RSL to lower a high resistanceassociated with the first state. Above the threshold, the externalstimulus maintains the metallic particles in sufficient formation toprovide the conductive path, leading to relatively low resistance of thesecond state. An analogous mechanism can control operation of the thirdstate in the bipolar context.

For a non-volatile filamentary-based resistive switching memory cell, anRSL can be selected to have sufficient physical defect sites therein soas to trap particles in place in the absence of a suitable externalstimulus, mitigating particle mobility and dispersion. This, in responseto a suitable program voltage applied across the memory cell, aconductive path or a filament forms through the RSL. In particular, uponapplication of a programming bias voltage, metallic ions are generatedfrom the active metal layer and migrate into the RSL layer. Morespecifically, metallic ions migrate to the voids or defect sites withinthe RSL layer. In some embodiments, upon removal of the bias voltage,the metallic ions become neutral metal particles and remain trapped invoids or defects of the RSL layer. When sufficient particles becometrapped, a filament is formed and the memory cell switches from arelatively high resistive state, to a relatively low resistive state.More specifically, the trapped metal particles provide the conductivepath or filament through the RSL layer, and the resistance is typicallydetermined by a tunneling resistance through the RSL layer. In someresistive-switching devices, an erase process can be implemented todeform the conductive filament, at least in part, causing the memorycell to return to the high resistive state from the low resistive state.More specifically, upon application of an erase bias voltage, themetallic particles trapped in voids or defects of the RSL become mobileand migrate back towards the active metal layer. This change of state,in the context of memory, can be associated with respective states of abinary bit. For an array of multiple memory cells, a word(s), byte(s),page(s), block(s), etc., of memory cells can be programmed or erased torepresent zeroes or ones of binary information, and by retaining thosestates over time in effect storing the binary information In variousembodiments, multi-level information (e.g., multiple bits) may be storedin such memory cells.

It should be appreciated that various embodiments herein may utilize avariety of memory cell technologies, having different physicalproperties. For instance, different resistive-switching memory celltechnologies can have different discrete programmable resistances,different associated program/erase voltages, as well as otherdifferentiating characteristics. For instance, various embodiments ofthe subject disclosure can employ a bipolar switching device thatexhibits a first switching response (e.g., programming to one of a setof program states) to an electrical signal of a first polarity and asecond switching response (e.g., erasing to an erase state) to theelectrical signal having a second polarity. The bipolar switching deviceis contrasted, for instance, with a unipolar device that exhibits boththe first switching response (e.g., programming) and the secondswitching response (e.g., erasing) in response to electrical signalshaving the same polarity and different magnitudes.

Where no specific memory cell technology or program/erase voltage isspecified for the various aspects and embodiments herein, it is intendedthat such aspects and embodiments incorporate any suitable memory celltechnology and be operated by program/erase voltages appropriate to thattechnology, as would be known by one of ordinary skill in the art ormade known to one of ordinary skill by way of the context providedherein. It should be appreciated further that where substituting adifferent memory cell technology would require circuit modificationsthat would be known to one of ordinary skill in the art, or changes tooperating signal levels that would be known to one of such skill,embodiments comprising the substituted memory cell technology(ies) orsignal level changes are considered within the scope of the subjectdisclosure.

The inventors of the subject application are familiar with additionalnon-volatile, two-terminal memory structures in addition to resistivememory. For example, ferroelectric random access memory (RAM) is oneexample. Some others include magneto-resistive RAM, organic RAM, phasechange RAM and conductive bridging RAM, and so on. Two-terminal memorytechnologies have differing advantages and disadvantages, and trade-offsbetween advantages and disadvantages are common. Thoughresistive-switching memory technology is referred to with many of theembodiments disclosed herein, other two-terminal memory technologies canbe utilized for some of the disclosed embodiments, where suitable to oneof ordinary skill in the art.

High density integration of memory often utilizes an array structure, inwhich multiple cells are connected along conductive lines of anintegrated chip, such as bitlines, wordlines, datalines, sourcelines,and the like. However, the inventors of the present disclosure believethat, while connecting multiple cells to a common conductive line canenhance memory density, such an arrangement can also result inelectrical problems such as leakage current (e.g., see FIG. 8, infra),reduced sensing margin, excess power consumption, and the like. This canbe particularly evident for memory cells programmed to a low resistancestate. As an illustrative example, an operational voltage applied to aselected conductive line, that is commonly connected to a target memorycell and several non-targeted memory cells, can result in significantcurrent flow at non-targeted memory cells in a low resistance state.Where a large number of non-targeted memory cells are connected to theselected conductive line (e.g., to achieve high memory density),significant power is consumed by this current. Additionally, capacitivevoltages on nearby conductive lines caused by the operational voltagecan result in leakage current from the nearby conductive lines to theselected conductive line. In addition to consuming additional power,this leakage current reduces sensing margin for a memory operationperformed on the target memory cell.

To reduce excess power consumption and leakage current in a memoryarray, a transistor may be connected to each memory cell, sometimesreferred to as a 1 transistor-1 memory cell architecture. The transistorcan be deactivated to shut off current through the memory cell,minimizing leakage current at that memory cell. However, addition of atransistor for each memory cell can significantly increase size of thememory cell (and reduce density of an associated array of memory). Somememory arrays balance memory density with leakage current, byimplementing a 1 transistor-n memory cell architecture, where n is aninteger greater than 1. In this architecture, increasing the number, n,of memory cells per transistor implements a trade-off between memorydensity and leakage current and power consumption. Thus, the inventorsunderstand that traditional attempts to achieve increased memory densitycan result in increased power consumption and associated joule heating,reduced sensing margin, and other problems.

Various embodiments of the present disclosure provide a selector device(e.g., a volatile switching device) configured to provide non-linearcurrent-voltage (I-V) response for a memory cell (e.g., a non-volatileswitching device) associated with the selector device. In particular,the non-linear I-V response can significantly reduce leakage current atthe associated memory cell. Further, the selector device can be amonolithic solid state construct fabricated in conjunction with theassociated memory cell that does not substantially increase the size ofthe memory cell. In the context of resistive memory cell technology, thedisclosed selector device can facilitate a 1 transistor-n resistor(1T-nR) architecture with high memory density. In some embodiments, thenumber of memory cells, n, per transistor can be 512, 1024, or evenlarger, without significantly impacting leakage current of a memoryarray. Accordingly, the disclosed selector device can facilitate highmemory densities with low leakage current, low power consumption andgood sensing margin.

Referring now to the drawings, FIG. 1 illustrates a block diagram of anexample selector device 100 according to one or more embodiments of thepresent disclosure. Selector device 100 can be a two-terminal deviceconfigured to be operable in response to a suitable electric signalapplied at one or more of two terminals of selector device 100. Invarious disclosed embodiments, selector device 100 can have a non-linearI-V response, in which selector device 100 exhibits current within afirst range in response to a first range of voltage magnitudes, andcurrent within a second range (e.g., much higher in magnitude than thefirst range) in response to a second range of voltage magnitudes (e.g.,see FIGS. 5 and 6, infra). The first range of voltage magnitudes andsecond range of voltage magnitudes can be distinguished, as one example,by a threshold voltage, or a threshold range of voltages (e.g., havingmagnitude(s) between the first range of voltage magnitudes and thesecond range of voltage magnitudes). In further embodiments, selectordevice 100 can be fabricated in series with a two-terminal memory device(not depicted, but see FIGS. 7 and 8, infra) as part of a monolithicfabrication process (e.g., photolithographic process, mask and etchingprocess, and so forth). In these latter embodiments, selector device 100can be configured to provide a non-linear I-V response for thetwo-terminal memory device, reducing leakage current and lowering powerconsumption, while facilitating increased memory density for an array ofsuch memory cells in series with respective ones of selector device 100.For instance, in the case of a two-terminal resistive memory cell,selector device 100 can facilitate a high density 1T-nR memory arraywith relatively high values for n, while mitigating leakage current andreducing power consumption for the 1T-nR memory array. In variousembodiments, selector device 100 may be embodied as a FAST™ selectordevice, currently under development by the current assignee of thepresent patent application.

Selector device 100 is depicted by FIG. 1 to have a top electrode 102and a bottom electrode 106. Top electrode 102 and bottom electrode 106are electrical conductors, and are comprised of materials suitable tofacilitate conduction of current. In one or more embodiments, topelectrode 102 and bottom electrode 106 can comprise a material(s)providing or facilitates provision of mobile atoms or ions in responseto a suitable stimulus. Examples of suitable stimuli can include anelectric field (e.g. a programming voltage), joule heating, a magneticfield, or other suitable stimuli for directed or partially directedparticle motion. In at least one embodiment, particle mobility can be inresponse to undirected or partially undirected dispersion, or similarphenomena.

Examples of suitable materials for top electrode 102 or bottom electrode106 can include a noble metal (e.g., Ag, Pd, Pt, Au, etc.) or a metalalloy containing noble metal in part (e.g., Ag—Al, Ag—Pd—Cu, Ag—W,Ag—Ti, Ag—TiN, Ag—TaN, and so forth). A noble metal or alloy thereof canbe utilized to facilitate mitigated interaction between top electrode102 or bottom electrode 106 and a selector layer 104, for instance. Thismitigated particle interaction (e.g., mitigating or avoiding chemicalbonding of top electrode 102 or bottom electrode 106 particles withparticles of selector layer 104) can facilitate improved longevity andreliability for selector device 100, as one example. Another example ofa suitable material for top electrode 102 or bottom electrode 106 caninclude a material with relatively fast diffusing particles. Fasterdiffusion can include, for instance, a capacity to move among defectsites (e.g., voids or gaps in molecular material) within a solid,facilitating dispersion of the relatively fast diffusion particlesabsent an aggregating force, for instance. Materials with relativelyfast diffusing particles can facilitate fast state switching of selectordevice 100 (e.g., from a non-conductive state to a conductive state), atlower bias values. Examples of suitable fast diffusing materials caninclude Ag, Cu, Au, Co, Ni, Al, Fe, or the like, suitable alloysthereof, or suitable combinations of the foregoing.

In at least one embodiment, top electrode 102 can be comprised of thesame material or substantially the same material as bottom electrode106. In other embodiments, top electrode 102 and bottom electrode 106can be different materials. In still other embodiments, top electrode102 and bottom electrode 106 can be at least in part the same material,and in part different materials. For instance, top electrode 102 couldcomprise a suitable conductive material, and bottom electrode 106 couldat least in part comprise an alloy of the suitable conductive material,or the suitable conductive material in combination with another suitableconductor, as an illustrative example.

In addition to the foregoing, selector device 100 includes selectorlayer 104. In contrast to top electrode 102 or bottom electrode 106,selector layer 104 can be an electrical insulator or ionic conductor.Further, selector layer 104 can be a material (e.g., an oxide) at leastweakly permeable to particles of top electrode 102 or bottom electrode106. In some embodiments, selector layer 104 can be a non-stoichiometricmaterial. Examples of suitable materials for selector layer 104 caninclude SiO_(X), TiO_(X), AlO_(X), WO_(X), Ti_(X)N_(Y)O_(Z), HfOx, TaOx,NbOx, or the like, or suitable combinations thereof, where x, y and zcan be suitable non-stoichiometric values. In some embodiments, selectorlayer 104 can be a chalcogenide or a solid-electrolyte materialcontaining one or more of Ge, Sb, S, Te. In yet another embodiment, theselector material can comprise a stack of a plurality of the abovementioned materials (e.g. SiOx/GeTe, TiOx/AlOx). In at least oneembodiment of the present disclosure, selector layer 104 can be dopedwith a metal(s) during fabrication, to facilitate metal ion injectionfrom the top or bottom electrode.

In operation, a suitable electric signal can be applied to top electrode102 or bottom electrode 106 to induce a state change of selector device100. State change can be a change in resistance or conductivity, forinstance. As one illustrative example, a voltage, field, current, etc.,can be applied at top electrode 102 or bottom electrode 106 having atleast a threshold magnitude associated with inducing the state change ofselector device 100. In response to such a signal at the thresholdmagnitude, selector device 100 can transition from a non-conductingstate having a high electrical resistance and a first current (or afirst range of currents), to a relatively-conducting state having alower electrical resistance and a second current (or a second range ofcurrents). In various embodiments, a current ratio of the first currentto the second current can be at least about 1,000 or more. For instance,in one embodiment, the current ratio can be selected from a range ofcurrent ratios from about 1,000 to about 10,000. In another embodiment,the current ratio can be selected from a range of current ratios fromabout 10,000 to about 100,000. In yet another embodiment, the currentratio can be selected from a range of current ratios from about 100,000to about 1,000,000. In still other embodiments, the current ratio can beselected from a range of current ratios from about 1,000,000 to about10,000,000 or more. Other suitable current ratios can be provided for aselector device 100 in various other suitable embodiments.

FIG. 2 illustrates a block diagram depicting operational behavior of aselector device 200 in response to applied signals, according toadditional embodiments of the present disclosure. For instance, selectordevice 200 comprises a top electrode 202, selector layer 204 and bottomelectrode 206, as depicted. In at least some embodiments, selectordevice 200 can be substantially similar to selector device 100 of FIG.1, infra, although the subject disclosure is not so limited.

At the top of FIG. 2, selector device 200 is illustrated with a firstsignal 202A applied to selector device 200. First signal 202A is greaterthan a threshold magnitude associated with non-linear I-V response ofselector device 200. In various embodiments, the threshold magnitude maybe embodied as a narrow range of threshold magnitudes (e.g., see below).It should be appreciated that reference herein to a threshold magnitude(e.g., voltage magnitude) associated with a non-linear I-V response of aselector device could include a narrow range of threshold magnitudes(e.g., a range of voltage values) over which an I-V response transitionsfrom linear (or approximately linear) behavior, to non-linear behavior.The range of magnitudes can vary as suitable for different sets ofmaterials, arrangement of such materials, characteristics of suchmaterials (e.g., thickness, area, conductivity, etc.), or the like,selected for components of the selector device.

Although first signal 202A is depicted as a voltage, e.g., where topelectrode voltage V_(TE) is greater than a first threshold voltageV_(TH1) of selector device 200, in other embodiments first signal 202Acan comprise other signals inducing particle mobility of particles oftop electrode 202 or bottom electrode 206, such as an electric field, acurrent, or even a temperature associated with joule heating. Inaddition to the foregoing, first signal 202A can be of a first polarity(e.g., at least in the electrical sense). For instance, first signal202A can have a positive gradient applied from top electrode 202 tobottom electrode 206 (e.g., a positive voltage or field at top electrode202 and ground or negative voltage or field at 206, current flow fromtop electrode 202 to bottom electrode 206, and so forth).

In response to first signal 202A (top electrode 202 relative to bottomelectrode 206), particles of top electrode 202 (or bottom electrode 206)can form a conductive path(s), or filament(s), within selector layer 204as depicted. In some embodiments, the particles can migrate intoselector layer 204 from top electrode 202 (or bottom electrode 206) inresponse to first signal 202A. In other embodiments—for instance whereselector layer 204 is doped with metallic particles—particles withinselector layer 204 can be ionized or aligned (e.g., spatially organizedalong the conductive path(s)) in response to first signal 202A. In stillother embodiments, particles can migrate from top electrode 202 (orbottom electrode 206) in combination with existing particles withinselector layer 204 being ionized and aligned in response to first signal202A, to form the conductive path(s) if the selector layer is doped withmetal particles. Formation of the conductive path(s) can facilitatetransition from a non-conductive state to a conductive state, associatedwith non-linear I-V response of selector device 200. Moreover, suitableformation of the conductive path(s) can be in response to a magnitude offirst signal 202A meeting or exceeding a first threshold magnitude.Thus, the first threshold magnitude is associated with causing thetransition to the conductive state.

At the bottom of FIG. 2, selector device 200 observes a second signal202B applied to top electrode 202 (relative to bottom electrode 206).Second signal 202B can have a magnitude less than the first thresholdmagnitude (e.g., V_(TE)<V_(TH1) e.g. V_(TE)≈0V), and in responseselector device 200 can transition from the (highly) conductive state tothe (relatively) non-conductive state. Again, in various embodiments,the first threshold magnitude may span a narrow range of magnitudes. Aconductive path(s) formed in response to first signal 202A candissipate, at least in part, in response to second signal 202B, asdepicted within selector layer 204 in the bottom of FIG. 2, or inresponse to removal of the first signal 202A. Dissipation can occur as aresult of particle tendency to migrate within or out of selector layer204, when an external force (e.g., second signal 202B) is ofinsufficient strength to hold the particles in the conductive path(s)through selector layer 204, from top electrode 202 through bottomelectrode 206. Thus, in one embodiment below the lowest thresholdmagnitude from a narrow range of magnitudes, the conductive path(s) isat least in part deformed, whereas at or above the highest thresholdmagnitude from the narrow range of magnitudes, the conductive path(s)can be formed sufficiently enough to cause the conductive state forselector device 200. To reiterate the above, in various embodimentsherein, it should be understood that reference to a threshold voltagemay actually refer to a set of threshold voltages (e.g., within a narrowrange of voltages) associated with formation and deformation of aconductive path.

As described above, selector device 200 can transition from thenon-conductive state to the conductive state, and back to thenon-conductive state, in a volatile manner. In other words, selectordevice 200 can be in the conductive state in response to the firstsignal 202A having the first threshold magnitude being applied toselector device 200. Selector device 200 can be in the non-conductivestate in response to the second signal 202B having less than the firstthreshold magnitude being applied to the selector device 200.

In some embodiments, selector device 200 can be combined in electricalseries with a two-terminal memory cell (e.g., a resistive switchingmemory, etc.). Selector device 200 can provide a non-linear I-Vcharacteristic for a two-terminal memory cell when provided in seriesthere with. Moreover, the non-linear I-V characteristic can be providedwhether the two-terminal memory cell is in a conductive state ornon-conductive state. For instance, a signal below the first thresholdmagnitude will cause selector device 200 to be in the non-conductivestate. In the non-conductive state, selector device 200 will resistcurrent through the series combination of selector device 200 and thetwo-terminal memory cell when the signal is below the first threshold.When the signal is equal to or above the threshold magnitude, selectordevice 200 will be conductive, and a state of the two-terminal memorycell can determine electrical characteristics of the series combinationof: selector device 200 and the two-terminal memory cell. Thus,activating selector device 200 will facilitate operational access to thetwo-terminal memory cell. Deactivating selector device 200 will resistoperational access to the two-terminal memory cell (e.g., by resistingcurrent through the series combination, and by dropping a majority ofthe voltage applied across the series combination, etc.). Becauseselector device 200 is volatile, and in the non-conducting state in theabsence of a signal having the first threshold magnitude, thetwo-terminal memory cell is inaccessible and retains information (e.g.,retains a current state thereof). Selector device 200, on the otherhand, provides a non-linear I-V response for the series combination,resisting leakage current and facilitating a memory array having highdensity.

FIG. 3 illustrates a block diagram depicting operational behavior of anexample selector device 300 according to further aspects of the subjectdisclosure. Selector device 300 can be substantially similar to selectordevice 100 or selector device 200, in one or more embodiments. However,the subject disclosure is not so limited.

Operational behavior of selector device 300 is illustrated in responseto signals of a second polarity, different from the first polarity offirst signal 202A and second signal 202B, described with respect to FIG.2, supra. For instance, the second polarity can be opposite orapproximately opposite the first polarity, in various embodiments. As anillustrative example, the second polarity can comprise a signal gradient(e.g., voltage gradient, current gradient, joule heating gradient, etc.)that is greater value measured from bottom electrode 306 and lesservalue measured from top electrode 302.

At the top of FIG. 3, a first signal 302A having magnitude equal to orgreater than a second threshold magnitude (or second range of thresholdmagnitudes, as suitable) is applied at bottom electrode 306 relative totop electrode 302. Particles of bottom electrode 306 migrate within andthrough a selector layer 304 in response to first signal 302A. Thesecond threshold magnitude is associated with suitable formation of aconductive path(s) across selector layer 304, from bottom electrode 306to top electrode 302, to induce a conductive state for selector device300. Note that in some embodiments, the second threshold magnitude (orrange of magnitudes) can be different (different values) from the firstthreshold magnitude (or range of magnitudes) associated with formationof conductive path(s) from top electrode 202 relative to bottomelectrode 206 as depicted by FIG. 2, supra. Difference in magnitude canoccur, for instance, where the top electrode and bottom electrode areformed of different materials having different particle mobility,different ion strength, different size, different shape, or the like.Said differently, employing different materials, sequences of materials(e.g., adding an addition layer—such as a barrier layer—between selectorlayer 304 and top electrode 302, or bottom electrode 306), materialproperties or characteristics for top electrode 302 or bottom electrode306 can lead to different threshold voltages associated with filamentformation from top electrode 202 to bottom electrode 206 (as depicted inFIG. 2) as compared with filament formation from bottom electrode 306 totop electrode 302 (as depicted in FIG. 3).

As depicted by FIG. 3, formation of the conductive path(s) can comprisesuitable particles of bottom electrode 306 migrating through selectorlayer 304, from bottom electrode 306 to top electrode 302, orpre-existing metal particles in selector layer 304 aligning/migrating toform the conductive path(s) (e.g., where the selector layer is dopedwith metal particles). At the bottom of FIG. 3, a second signal 302Bhaving magnitude less than the second threshold magnitude (or range ofmagnitudes) is applied at bottom electrode 306. In response to thesecond signal, particles of the conductive path(s) disperse throughselector layer 304 (or toward/into bottom electrode 306), at least inpart deforming the conductive path(s). This induces a non-conductivestate for selector device 300. Thus, in one embodiment below the lowestthreshold magnitude from a narrow range of magnitudes, the conductivepath(s) is at least in part deformed, whereas at or above the highestthreshold magnitude from the narrow range of magnitudes, the conductivepath(s) can be formed sufficiently enough to cause the conductive statefor selector device 300. To reiterate the above, in various embodimentsherein, it should be understood that reference to a threshold voltagemay actually refer to a set of threshold voltages (from a narrow rangeof voltages) depending on whether a conductive path is formed ordeformed.

In other embodiments, if polarity of the voltage source is defined aspositive to negative relative to top electrode 302 and bottom electrode306, below the lowest threshold magnitude from a narrow range ofmagnitudes, the conductive path(s) can be formed sufficiently enough tocause the conductive state for selector device 300, whereas at or abovethe highest threshold magnitude from the narrow range of magnitudes, theconductive path(s) is at least in part deformed. Examples of this willbe illustrated, below.

In various embodiments, selector device 300 can have the propertiesdescribed above with respect to selector device 200 in response to asignal of the first polarity. Thus, selector device 300 can form aconductive path(s) comprising particles from top electrode 302 extendingthrough selector layer 304 in response to a signal of the firstpolarity, and can form a second conductive path(s) comprising particlesfrom bottom electrode 306 extending through selector layer 304 inresponse to a signal of the second polarity. In at least someembodiments, the conductive path can at least in part comprise particlesof bottom electrode 306 (e.g., near to a boundary of bottom electrode306), and likewise the second conductive path can at least in partcomprise particles of top electrode 302 (e.g., near to a boundary of topelectrode 302). Thus, selector device 300 can have a first thresholdmagnitude to facilitate transition to a first conducting state along thefirst polarity, and a second threshold magnitude to facilitatetransition to a second conductive state along the second polarity. Thisoperation can be implemented in conjunction with a bipolar memory cell,providing non-linear I-V characteristics for first polarity signals aswell as for second polarity signals. In pragmatic terms, bidirectionalnon-linear I-V characteristics can facilitate resistance to leakagecurrents from either positive or negative polarity signals. Thus, theseries combination of selector device 300 and a two-terminal memory cellcan mitigate leakage current resulting from a programming signal or readsignal (e.g., having a first polarity) or an erase signal (e.g., havingthe second polarity). In at least some embodiments, it should beappreciated that this description of selector device 300 (and othersuitable descriptions for FIG. 3), can have analogous applicability toselector device 200 of FIG. 2, supra. Also, the reverse is true;illustrative embodiments described with respect to selector device 200can be applicable to selector device 300 in suitable embodiments.Accordingly, the example embodiments described for FIGS. 3 and 2 shouldbe considered interchangeable, where suitable.

In various embodiments, selector device 300 can be operated within a setof operational parameters. In some embodiments, the set of operationalparameters can be selected to maintain volatile state-switching ofselector layer 304 (e.g., by forming a relatively weak filament, whichat least in part deforms below a threshold signal magnitude), provideswitching longevity, achieve a target power consumption, or the like, ora suitable combination thereof. In some embodiments, current throughselector device 300 (and, e.g., the series combination of selectordevice 300 and a two-terminal memory cell) can be limited to a maximumcurrent value.

For instance, the maximum current value can be limited to 300 microamps(μA) or below, 300 μA or below, or another suitable maximum value. Inother embodiments, selector layer 304 can have a thickness maintainedwithin a target range of thicknesses. For example, the thickness ofselector layer 304 can be from about 0.5 nanometers (nm) to about 50 nm.In various embodiments, based upon current experimental data, typicalthicknesses which provide surprisingly effective results based upon athreshold voltage of about 1 volt may be within a range of about 1 toabout 20 nm, and more specifically about 1 nm to about 10 nm. In atleast one embodiment, the thickness of selector layer 304 (or, e.g.,selector layer 204 of FIG. 2, infra) can be selected to provide a signalthreshold magnitude (e.g., voltage threshold, current threshold, fieldstrength threshold, etc.) associated with state-switching of selectordevice 300 to have a target value, or be within a target range. As oneillustrative example, the thickness can be selected to provide athreshold voltage associated with state-switching to be between about0.1 volts and about 4 volts. Maintaining the threshold voltage at atarget value can mitigate or avoid formation of a non-volatile filament.

In some embodiments, a stoichiometric value(s) of material utilized forselector layer 304 (or selector layer 204) can be provided at a targetvalue. For instance, a stoichiometric value for ‘x’ for a SiOx selectorlayer 304 (or selector layer 204) can be between about 0.5 and about 2.In at least one embodiment, the stoichiometric value can be selected toachieve a target width for a conductive path (e.g., filament) throughselector layer 304 (or selector layer 204). In some embodiments,increasing stoichiometric value(s) of the material utilized for selectorlayer 304 (or selector layer 204) can reduce defect density of selectorlayer 304 or 204 (e.g., density of dangling bonds, density of particlevoids, and so forth), and the stoichiometric value can be selected toachieve a target defect density to provide the target width for theconductive path. In at least one disclosed embodiment, selector layerthickness and stoichiometric value can be respectively selected toachieve a target trade-off between maximum threshold voltage and maximumdefect density.

FIG. 4 illustrates a block diagram of an example solid state switchingdevice 400 according to alternative or additional aspects of the presentdisclosure. Solid state switching device 400 can be configured tooperate as a volatile switching device in series with a two-terminalmemory device, in one or more embodiments. In other embodiments, solidstate switching device 400 can be configured to operate as a stand alonesolid state electronic component, such as a volatile switch, or as anelectronic component in conjunction with one or more other electronicdevices (e.g., operable in conjunction with one or more CMOS devicesfabricated in or on a CMOS substrate).

As depicted, solid state switching device 400 can comprise a topelectrode 402, an ion conductor layer₁ 404, a selector layer 406, an ionconductor layer₂ 408 and a bottom electrode 410. In various alternativeembodiments, solid state switching device 400 can comprise one oranother of ion conductor layer₁ 404 or ion conductor layer₂ 408, ratherthan both. In alternative or additional embodiments, top electrode 402,selector layer 406 and bottom electrode 410 can be substantially similarto the similarly named layers of FIGS. 3 and 2, supra, however thesubject disclosure is not so limited, and different materials orcharacteristics can be associated with selector layer 406—selected forsuitability when selector layer 406 is adjacent to ion conductor layer₁404 or ion conductor layer₂ 408—within the scope of the presentdisclosure.

Top electrode 402 or bottom electrode 410 can comprise a noble metal, asuitable metal alloy containing noble metal in part, a fast diffusingmaterial (e.g., Cu, Al, Ti, Co, Ni, Ag, etc.) or suitable alloys of thefast diffusing metal, or the like, or a suitable combination thereof. Invarious embodiments, top electrode 402 or bottom electrode 410 can be anactive metal, whereas in other embodiments top electrode 402 or bottomelectrode 410 can be an integrated circuit wiring metal (e.g., W, Al,Cu, TiN, TiW, TaN, WN, and so forth). In some embodiments, top electrode402 and bottom electrode 410 can be the same material; in otherembodiments, top electrode 402 and bottom electrode 410 can be differentmaterials.

Further to the above, solid state switching device 400 can comprise aselector layer 406. Selector layer 406 can comprise an electricallyresistive material that is weakly permeable to ions of top electrode 402or bottom electrode 410. Weak permeability can facilitate reliabledeformation or dispersion of conductive ions within selector layer 406,in response to a signal below a threshold magnitude, as describedherein. In other words, weak permeability can facilitate volatileformation and deformation of a conductive path(s) within selector layer406.

Further to the above, solid state switching device 400 can comprise ionconductor layer₁ 404 and ion conductor layer₂ 408. Ion conductor layer₁404 or ion conductor layer₂ 408 can comprise a solid electrolyte (e.g.,Ag—Ge—S, Cu—Ge—S, Ag—Ge—Te, Cu—Ge—Te, GeSb, etc.), a metal-oxide alloy(e.g., AgSiO₂, CuAl2Ox, and so forth). In some embodiment, solid stateswitching ion conductive layer₁ 404 can depend at least in part on adiffusivity metric of ions of top electrode 402. In another embodiment,presence of ion conductive layer₂ 408 can depend at least in part on adiffusivity metric of ions of bottom electrode 410. In furtherembodiments, ion conductor layer₁ 404 or ion conductor layer₂ 408 can beselected to yield faster ion generation (hence faster switching or lowervoltage switching) for selector layer 406 as compared with top electrode402 or bottom electrode 408.

FIG. 5 illustrates a diagram of an example electrical response 500 for aselector device according to one or more additional embodimentsdescribed herein. Particularly, electrical response 500 can beassociated with a selector layer of a selector device described herein.As depicted, a vertical axis of electrical response 500 depicts current(in Amps [A]) conducted across the selector device (e.g., from a topelectrode to a bottom electrode), and a horizontal axis of electricalresponse 500 depicts a voltage (in Volts [V]) applied across theselector device. Note that the left side of the horizontal axis isnegative voltage and the right side of the horizontal axis is positivevoltage (measured at the top electrode, for example).

A sharp non-linear inflection point in current value occursapproximately at a positive threshold voltage Vth₁ and approximately ata negative threshold voltage Vth₂. In some embodiments, positivethreshold voltage Vth₁ can have substantially the same or the samevoltage magnitude as negative threshold voltage Vth₂. In otherembodiments, however, positive threshold voltage Vth₁ can have adifferent magnitude from negative threshold voltage Vth₂.

In various embodiments, the blue arrow labeled selector “off” current502 indicates the inflection point in current, below which current dropsoff more slowly versus voltage and above which current increases veryquickly with increasing voltage, up to a current compliance level 506(e.g., that was set by a tester or external input). The selector “on”current 504 is achieved at slightly higher voltage than Vth₁ or Vth₂. Inthe example in FIG. 5, between 0 and about 1.5 volts, the off-statecurrent is illustrated to be lower than about 1E-9 amps. In otherexperiments, lower off-state currents have been achieved, for example,lower than 1E-10 amps, lower than 1E-11 amps, or the like in embodimentswith inflection point voltages of approximately 1 volt.

As mentioned above, Vth1 may be similar or different from Vth2. Further,the amount of current associated with the inflection point in thereverse polarity (e.g. V<0) may be different from the current associatedwith the inflection point for V>0. In the example in FIG. 5, theoff-state current may be lower than about 5E-9. In other experiments,lower off-state currents have been achieved, for example, lower than1E-10 amps, lower than 1E-11 amps, or the like in embodiments withinflection point voltages of approximately −0.5 volt. In variousembodiments, electrical response 500 can be characterized by arelatively steep change in current as a function of voltage, uponvoltage meeting or exceeding an upper range for Vth₁ and prior tocurrent compliance, compared to voltage less than a lower range for Vth₁(Vth₁ referring to a narrow range of voltages). For instance, electricalresponse 500 can have a current increase measured as a function ofcurrent decade (e.g., an order of magnitude change in current) pervoltage, or I_(DECADE)/V, or as a function of voltage per currentdecade, V/I_(DECADE). In some embodiments, electrical response 500 canincrease between about 3.5 decades and about 4 decades per 100milliVolts (mV), or between about 0.035 decades/mV and about 0.04decades/mV, for a subset of voltages that are equal to or greater thanVth₁.

Alternatively, electrical response 500 can be characterized by a changebetween about 25 and about 29V/decade between the lowest value of Vthand the highest value of Vth. In other embodiments, electrical response500 can have an electrical response 500 (e.g., in response to a negativevoltage) of between about 0.030 decades/mV and about 0.040 decades/mVfor a subset of negative voltages that are equal to or less than Vth₂.Stated differently, electrical response 500 can be between about 25mV/decade and about 33 mV/decade for a subset of voltages that arewithin the range of Vth₂. In other experiments, the electrical responsehas been measured to be about 17 mV/decade (a Vth range of about 100 mVover 6 decades) or about 0.06 decades/mv. In such embodiments, thenominal Vth value is on the order of about 1 volt. In light of thepresent disclosure, electrical responses 500 within a range of about 10mV/decade to about 100 mV/decade are now achievable. Further, electricalresponses on the order of 0.1 mV/decade to about 0.01 mV/decade are nowbelieved to be enabled.

Nominal threshold voltage magnitudes for electrical response 500 arebetween about 1.5 volts and about 2 volts in magnitude. In someembodiments, the nominal threshold voltage magnitudes can be betweenabout 1.5 volts and about 1.8 volts in magnitude. For these ranges ofthreshold voltages, in FIG. 5, a difference in magnitude of selector“off” current 502 and selector “on” current 504 is about four orders ofmagnitude (e.g., 1×10⁴, or 10,000) for positive voltages, and aboutthree and a half orders of magnitude (e.g., 5×10³, or 5,000) fornegative voltages. In an embodiment with lower threshold voltages Vth₁and Vth₂, a much higher difference in magnitude of selector “off”current 502 versus selector “on” current 504 can be achieved. Forexample, in embodiments where the nominal threshold voltage Vth₁ isapproximately 1.1 volts, the electrical response is about 16 mV/decade.

In various embodiments, electrical response 500 can vary for differentselector devices. For instance, variation in materials employed for aselector device can result in variations in electrical response 500,including selector “off” current 502, selector “on” current 504 andpositive and negative threshold voltages. In another embodiment,thickness of a selector material layer can additionally affectelectrical response 500. Accordingly, a target electrical response 500can to some extent be achieved by selecting a suitable top electrodematerial, selector layer material or thickness, or bottom electrodematerial for a disclosed selector device.

FIG. 6 depicts a diagram of an electrical response 600 for a selectordevice according to additional embodiments of the subject disclosure. Avertical axis of electrical response 600 displays current (A) conductedby the selector device, and a horizontal axis of electrical response 600displays voltage (V) applied across the selector device. A selector“off” current 602 is illustrated with very sharp non-linear response,from about 1×10⁻¹¹ amps (10.0×10⁻¹²) to about 1×10⁻⁴ amps (100.0×10⁻⁶)with an on/off ratio within a range of about 6 to about 10 orders ofmagnitude, for a selector “on” current 604, at current compliance 606.In one example, a current ratio of “on” current to “off” current ofseven orders of magnitude, or a ratio of 10,000,000 is achieved. Thisratio is achieved at a nominal positive threshold voltage, or Vth₁, ofjust under 300 millivolts, and a nominal negative threshold voltage, orVth₂, of about −200 millivolts. By utilizing a selector device 600 withsuitable selector and top electrode or bottom electrode material(s), asmaller ratio of “on” current to “off” current can be achieved. Forinstance, in one embodiment, a current ratio in a range of 1,000,000 toabout 10,000,000 can be achieved. In another embodiment, a current ratioin a range of about 100,000 to about 1,000,000 can be achieved. In yetanother embodiment, a current ratio in a range of about 10,000 to about100,000 can be achieved. In still another embodiment, a current ratio ina range of about 1,000 to about 10,000 can be achieved. In at least onedisclosed embodiment, a current ratio equal to about 100,000 or largercan be achieved. In at least one further embodiment, a current ratio aslarge as about 10.0×10⁻⁹ can be achieved.

Electrical response 600 can also be characterized by increase in currentas a function of voltage, or vice versa. For a subset of voltages equalto or greater than Vth₁, electrical response 600 can have an electricalresponse 600 between about 3.5 mV/decade and about 14 mV/decade in anembodiment. In another embodiment, electrical response 600 can have anelectrical response 600 between about 0.07 decades/mV and about 0.25decades/mV for the subset of voltages equal to or greater than Vth₁. Infurther embodiments, for a second subset of voltages equal to or lessthan Vth₂, electrical response 600 can be between about 7 mV/decade andabout 7.5 mV/decade. In another embodiment, for the second subset ofvoltages, electrical response 600 can be between about 0.15 decades/mVand about 0.12 decades/mV. In at least one additional example,electrical response of a disclosed selector device can be about 1.5mV/decade, or about 0.7 decades/mV. In a further embodiment, theelectrical response can be selected from a range of about 1 mV/decadeand about 60 mV/decade. In yet another embodiment, the electricalresponse can be selected from a range of about 1 decade/mV and about0.15 decades/mV.

FIG. 7 illustrates a block diagram of an example memory device 700according to further embodiments of the present disclosure. Memorydevice 700 can comprise a two-terminal memory component 702 electricallyin series with a selector device 706. Additionally, memory device 700can comprise a first terminal 702A and a second terminal 702B forapplying an operation signal across memory device 700 (e.g., a readsignal, an erase signal, a program signal, a rewrite signal, and soforth).

Memory device 700 can be a non-volatile, two-terminal switching element.Examples can include a resistive memory, a resistive-switching memorysuch as a resistive random access memory (RRAM), a phase-change memory(PCRAM), a magneto-resistive memory (MRAM), a ferroelectric memory(FeRAM), organic memory (ORAM), conductive bridging memory (CBRAM),one-time programmable memory (OTP) or the like. In particularembodiments, memory device 700 can be a bipolar memory device.Accordingly, memory device 700 can be programmed or written in responseto a signal(s) of a first polarity. Further, memory device 700 can beerased in response to a signal(s) of a second polarity. According tovarious embodiments, selector device 706 can be configured as a bipolarswitching device. In such embodiments, selector device 706 can beswitched from a non-conducting state to a conducting state in responseto a signal of the first polarity exceeding a first polarity thresholdmagnitude, threshold₁ (e.g., a first polarity threshold voltage Vth₁,and so on). Further, selector device 706 can be switched from thenon-conducting state to the conducting state in response to a secondsignal of the second polarity exceeding a second polarity thresholdmagnitude, threshold₂ (e.g., a second polarity threshold voltage Vth₂,or the like).

In various embodiments, selector device 706 can have a greaterelectrical resistance in the non-conducting state than an associatedoff-state (e.g., erased state) electrical resistance of two-terminalmemory component 702. Likewise, selector device 706 can have a greaterelectrical conductivity in the conducting state than an associatedon-state (e.g., program state) electrical conductivity of two-terminalmemory component 702. Accordingly, selector device 706 can serve as anactivation/deactivation component for memory device 700, resistingmemory operations at two-terminal memory component 702 when in anon-conducting state, and enabling memory operations at two-terminalmemory component 702 when in a conducting state. For embodiments inwhich two-terminal memory component 702 and selector device 706 arebipolar switching devices, the activation/deactivation effect ofselector device 706 can occur in response to signals of a first polarity(e.g., read signals, program signals, etc.) as well as signals of asecond polarity (e.g., erase signals, and so forth).

In at least one embodiment, activation/deactivation of memory device 700can be characterized by a voltage divider arrangement. For instance,when in the off-state, selector device 706 can be selected to have asuitably larger resistance than two-terminal memory component 702.Therefore, when in the off-state, selector device 706 can be configuredto drop most of a voltage applied between the two end terminals 702A and702B, thereby insulating two-terminal memory component 702 from avoltage suitable for programming, erasing or reading two-terminal memorycomponent 702. A voltage above the first polarity threshold magnitudewill turn selector device 706 to the on-state, lowering resistance ofselector device 706 to a lower resistance than two-terminal memorycomponent 702. This enables a signal applied to memory device 700 toaffect two-terminal memory component 702. For the embodiments in whichselector device 706 is a bipolar device, selector device 706 can respondsimilarly with respect to a signal of the second polarity below thesecond polarity threshold magnitude (insulating two-terminal memorycomponent 702 from such a signal) or above the second polarity thresholdmagnitude (exposing two-terminal memory component 702 to such signal),as described above with respect to signals of the first polarity. Insome embodiments, however, selector device 706 can respond at least inpart differently for first polarity and second polarity signals. As oneexample, selector device 706 can have a different first thresholdmagnitude in response to first polarity signals, as compared with secondthreshold magnitude in response to second polarity signals. In anotherexample, selector device 706 can have a different non-linear response tofirst polarity signals as compared with an associated non-linearresponse to second polarity signals, or the like, or suitablecombinations thereof.

The inventors of the present disclosure believe that memory device 700can provide significant advantages over other proposed or theorizedmechanisms for providing high density memory for advanced technologynodes. As described herein, selector device 706 can provide a non-linearI-V response for a two-terminal memory component 702. The non-linearresponse can greatly mitigate leakage current (e.g., see FIG. 9, infra)for 1T-nR memory arrays having large values for n (e.g., where n is 512,1024, or even larger).

In addition, selector device 706 can provide significant advantages overother non-linear electronic components, such as a solid state diode. Asone example, selector device 706 can be fabricated at relatively lowtemperature, whereas solid state diodes generally require higher than500 degrees Celsius (° C.). High temperatures can prevent back-enddevice fabrication on top of an integrated circuit (e.g., back end ofline processing), where such temperatures exceed a thermal budget of theintegrated circuit. Selector device 706 can be fabricated within thermalbudgets of many integrated circuits, whereas solid state diodesgenerally cannot. In some embodiments, selector device 706 can befabricated below 400° C.; in other embodiments, selector device 706 canbe fabricated below 300° C.; in still other embodiments selector device706 can be fabricated as low as 200° C. or even lower. Thesetemperatures can enable the back-end fabrication of memory device 700 onmany integrated circuits comprising pre-fabricated CMOS devices, siliconon insulator (SoI) devices, or the like, or suitable combinationsthereof (e.g., see FIG. 8, infra).

In addition to the foregoing, solid state diodes may not be fabricatedor operated reliably at 22 nm technology nodes or below. In contrast,selector device 706 can operate for 22 nm technology nodes in someembodiments; in additional embodiments selector device 706 can operatefor 14 nm technology nodes; in still other embodiments selector device706 can operate for 10 nm technology nodes, 7 nm technology nodes or 5nm technology nodes, etc. (or suitable half-nodes smaller than 22 nm).Furthermore, solid state diodes generally do not operate in a bipolarfashion, switching from high resistance to low resistance in response topositive polarity signals and negative polarity signals. Accordingly,solid state diodes cannot generally be used with bipolar memory forrewritable memory applications. Selector device 706 is not so limited,and can provide non-linear characteristics for bipolar memory,facilitating non-linear I-V response for program or read signals of afirst polarity, in addition to non-linear I-V response for erase signalsof a second polarity. Further to the above, selector device 706 can beutilized in a three-dimensional array of memory devices 700, in additionto two-dimensional arrays, providing much greater memory densities thantechnologies limited to two-dimensional arrays.

In an alternative or additional embodiment of the present disclosure,selector device 706 can comprise a selector material associated with afirst current in response to an applied voltage less than a thresholdvoltage associated with selector device 706. Further, the selectormaterial can be associated with a second current in response to anapplied voltage greater or equal to the threshold voltage. A ratio ofthe second current to the first current can be selected from a range ofratios from about 1,000 to about 10,000, in an embodiment(s). In anotherembodiment(s), the ratio of the second current to the first current canbe selected from a range of ratios from about 10,000 to about 100,000.In yet another embodiment(s), the ratio of the second current to thefirst current can be selected from a range of ratios from about 100,000to about 1,000,000. According to a further embodiment(s), the ratio ofthe second current to the first current can be selected from a range ofratios from about 1,000,000 to about 10,000,000.

According to other disclosed embodiments, selector device 706 cancomprise a top electrode 708 comprised of a first metal, and a bottomelectrode 716 comprised of a second metal. In various embodiments, thefirst metal can be similar to the second metal; whereas in at least oneembodiment the first metal can be the same as the second metal. Infurther embodiments, the first metal or second metal can be selectedfrom a group consisting of: an active metal, W, Al, Cu, TiN, TaN, WN,and TiW. In another embodiment(s), selector device 706 can comprise afirst ion conductor 710 or a second ion conductor 714. In anembodiment(s), first ion conductor 710 or second ion conductor 714 canbe selected from a group consisting of: an ion conductor, an electrolyte(e.g., a solid electrolyte), a chalcogenide, a metal oxide, and a metaloxide alloy.

According to additional embodiments, selector device 706 can comprise aselector layer 712. Selector layer 712 can comprise a selector materialconfigured to allow conductive ions to permeate within the selectormaterial of selector layer 712 in response to a voltage across topelectrode 708 and bottom electrode 716. In further embodiments, theselector material can comprise a material selected from a groupconsisting of: an insulator, a non-stoichiometric oxide, a solidelectrolyte, a chalcogenide, and a metal-doped material.

According to another embodiment(s), selector device 706 can have athreshold voltage of a first polarity or a second threshold voltage of asecond polarity that is about one half of a program voltage oftwo-terminal memory component 702. In such embodiment(s), a read voltageof the two-terminal memory component 702 can be smaller than the programvoltage and larger than the threshold voltage of the first polarity orthe second threshold voltage of the second polarity.

FIG. 8 illustrates a block diagram of a side view of an example memoryarchitecture 800 comprising multiple arrays of two-terminal memorydevices configured to mitigate leakage current on a conductor of thearray, according to one or more embodiments of the subject disclosure.In some embodiments, memory architecture 800 can facilitate improvedmemory densities even at advanced technology nodes (e.g., 22 nm andbelow). In other embodiments, memory architecture 800 can facilitatefabrication of high capacity, fast switching and high longevity memorymonolithically integrated with an integrated circuit comprisingpre-fabricated electronic components, at very low fabrication costs.

As depicted, memory device 800 can comprise a substrate 802. Substrate802 can be a silicon wafer, or other suitable insulated semiconductingmaterial utilized for fabrication of one or more electronic devices 804on, within or partially within substrate 802 (e.g., where the electronicdevices 804 can include electronic devices, SoI devices, or the like, ora suitable combination thereof). In the example of FIG. 8, electronicdevices 804 can be at least in part formed within substrate 802.Although electronic devices 804 are illustrated as being wholly withinsubstrate 802, it should be appreciated that electronic devices 804 canbe constructed at least in part on or above substrate 802 (e.g.,front-end-of-line process layers). For instance, one or more electronicdevices 804 can comprise a transistor having a source or drain contactformed within substrate 802, and a floating gate, or the like, in alayer above substrate 802. The one or more electronic devices 804 may bedriver circuits, logic circuits, processing devices, array logic, or thelike. Back-end of line processes can be formed within, or interspersedamong, one or more insulator 807 layers. Back-end of line processes cancomprise conductive layers, memory layers (e.g., resistive-switchinglayers, or other suitable two-terminal memory active region layer),selector layers, barrier layers, electrical contact layers, insulatorlayers, or the like, or suitable combinations thereof.

Memory device 800 can comprise one or more select transistor(s) 806 foractivating or deactivating memory cells 812 of memory device 800. Selecttransistor 806 can be connected through a first via layer, via₁ 808, toa first bitline, bitline₁ 810 associated with memory cells 812. Whenselect transistor 806 is activated, a suitable signal (e.g., programsignal, read signal, erase signal, etc.) can be applied through via₁ 808to bitline₁ 810. Bitline₁ 810 in turn is connected to respective firstcontacts of a first set of memory cells 812 (the lower set of memorycells depicted at FIG. 8). Deactivation of select transistor 806 canisolate bitline₁ 810 from the operation signal, resisting electricalcurrent on via₁ 808. Thus, select transistor 806 can serve as the 1Ttransistor in a 1T-nR memory architecture, where n is defined by anumber of memory cells 812 activated by select transistor 806.

Memory cells in the first (lower) array have respective first contactsconnected to bitline₁ 810, and respective second contacts connected torespective ones of wordlines 818. Note that respective memory cells 812comprise a selector component 814 in electrical series with a memorycomponent 816. Memory component 816 can comprise a two-terminalswitching device (e.g., resistive memory, phase-change memory,magneto-resistive memory, and so forth), such as described with respectto two-terminal memory component 702 of FIG. 7, supra. Likewise,selector component 814 can comprise a selector device as describedherein (e.g., see FIGS. 1, 2, 3, 4, 7, supra), having one or moreelectrodes, a selector layer and optionally one or more ion conductorlayers.

Additionally, it should be appreciated that the orientation of selectorcomponent 814 and memory component 816 can be reversed; for instance,the first array of memory cells 812 depicts selector component 814 belowmemory component 816, however a second array (top array) of memory cells812 depicts selector component 814 above memory component 816. It shouldbe appreciated that memory cells 812 are not limited to the depictedarrangement; in an alternative embodiment, memory cells 812 canuniformly have respective selector components 814 below respectivememory components 816; other embodiments can uniformly have respectiveselector components 814 above respective memory components 816; stillother embodiments can have a combination of the foregoing, and furtherembodiments can comprise non-uniform orientation of respective selectorcomponents 814 and memory components 816 for subsets of memory cells812.

A second array of memory cells 812 (top array) are connected atrespective memory components 816 to respective ones of wordlines 818,and at associated selector components 814 to a second bitline, bitline₂820. Bitline₂ 820 can be activated through a series of vias, including afirst layer via₁ 806 (activated by a select transistor), a second layervia₂ 822 and a third layer via₃ 824. In other embodiments, more or fewervias can be utilized to connect bitline₂ 820 with its associated selecttransistor 806.

In some embodiments, via₁ 806, via₂ 822, or via₃ 824 (referred tocollectively as via layers 806, 822, 824) can connect a bitline 810,820, or a wordline 818, source line, etc. (not depicted), to componentsof electronic devices 804 or two-terminal switching devices 812, as isknown in the art or is made known to one of ordinary skill in the art byway of the context provided herein. Via layers 806, 822, 824 cancomprise a metal, a conductive silicon-based material, and so forth. Insome disclosed embodiments, via layers 806, 822, 824 or other via layersnot depicted can be utilized to form one or more layers of non-linearmemory cell 812 (e.g., where one or more layers of memory component 814or selector component 816 can be fabricated at least in part inconjunction with a via layer 806, 822, 824).

It should be appreciated that memory device 800 can have arrays ofmemory cells 812 extrapolated in additional dimensions in a twodimension or three dimension array. For instance, memory device 800 cancomprise additional arrays of memory cells 812 in and out of the page ofFIG. 8. In further embodiments, memory device 800 can have additionallayers of bitlines and wordlines above bitline₂ 820, with respectivearrays of memory cells 812 there between, enabling increased numbers ofmemory cells 812 in the vertical direction.

Note that memory cells 812 are illustrated as having a verticalarrangement (e.g., memory component 814 above selector component 816),in other embodiments non-linear memory cell 812 can be arranged along anoblique angle. For instance, memory component 816, selector component814, or a subset of the solid state layers of the foregoing, can bearranged sequentially along a direction that is not perpendicular to atop surface of substrate 802. In at least one embodiment, memorycomponent 814 and selector component 816 can be arranged in a directionthat is parallel to, or near parallel to the top surface of substrate802, or other suitable direction. In such embodiments, wordlines 818 orbitline₁ 810 or bitline₂ 820 can be re-oriented (e.g., as a film or fillwithin a via) as suitable to accommodate the oblique orientation.

The inventors of the present disclosure understand that someconventional techniques for fabricating non-linear electronic componentscan involve quite high temperatures (e.g., 500° C., 600° C., or higher).The inventors understand these high temperature processes are generallyincompatible with advanced CMOS processing (e.g., where the maximumallowed process temperature is <370˜430C). Thus, the inventorsunderstand that manufacture of a memory device 800 could conventionallyrequire non-monolithic processes. The inventors believe thatnon-monolithic fabrication can be much more complex, however, requiringhigher costs, longer fabrication times, and greater overhead than amonolithic process, for instance. In contrast, monolithic fabricationcan merely involve a set of additional masks or etching processes toform non-linear memory cell 812 (or, e.g., interconnect layer(s) 806,via layers 810, 812, or metal conductor(s) 818) on a single integratedchip having electronic devices 804 pre-fabricated therein (or thereon),as one example.

FIG. 9 illustrates a block diagram of an example array 900 of memorycells, in additional embodiments of the present disclosure. Array 900can be a crossbar memory array, as depicted, comprising a first set ofconductors, bitlines 902, substantially parallel to a second set ofconductors, wordlines 904, with respective two-terminal memory devicesat intersections of respective bitlines 902 and wordlines 904. Array 900illustrates sneak path currents (also referred to herein as leakagecurrents) caused by a program supply signal applied to a selected one ofwordlines 904, in addition to sneak path currents caused byinter-bitline voltage potentials (e.g., capacitive voltages). Array 900illustrates problems associated with sneak path currents, and thereforeis useful to illustrate benefits of non-linear characteristics fortwo-terminal memory.

As mentioned above, array 900 comprises a set of bitlines 902substantially perpendicular to a set of wordlines 904. Where respectivebitlines 902A, 902B, 902C intersect one of the wordlines 904A, 904B,904C, a non-linear two-terminal memory cell is positioned, having afirst terminal connected to one of bitlines 902 and a second terminalconnected to one of wordlines 904. Further, a selected cell 906 is anon-linear two-terminal memory cell targeted for a program operation.Particularly, the program operation includes a program signal 910 ofabout three volts applied to wordline 904B. In some embodiments,intermediate signals of about 1.5 volts can be applied to non-selectedwordlines 904A, 904C, whereas in other embodiments wordlines 904A, 904Ccan be left floating. Additionally, bitline 902B is driven to zero volts(e.g., to provide a 3 volt potential difference across selected cell906), whereas bitlines 902A, 902C can be driven to 1.5 volts (or, e.g.,can be left floating in at least one embodiment). Capacitive couplingamong bitlines 902A, 902C and wordlines 904 will induce a voltage ontobitlines 902A, 902C greater than zero volts and less than three volts.

The program operation voltages can cause multiple sneak path currents;sneak paths caused by signal program 910, referred to as program sneakcurrents 912, and sneak paths on bitline 902B, referred to as bitlinesneak currents 914. Bitline sneak currents 912 are depicted by dashedlines, whereas the program sneak currents 912 are depicted by narrowsolid lines. Two paths are depicted for bitline sneak currents 914,through non-selected cells 908 on wordlines 904A, 904C. Each of thebitline sneak currents 914 share bitline 902B as a common component ofthe respective paths. Program sneak currents 912 propagate through theselected local wordline 904B, to bitlines 902A, 902C, respectively.

Note that program supply current sneak paths on wordlines other than onthe selected wordline 904B of memory array 900 are not depicted. If thenon-selected wordlines 904A, 904C are allowed to float, capacitivecoupling induces a voltage on non-selected wordlines 904A, 904C whichcan approach 1.5 volts in some embodiments (e.g., depending oninter-wordline capacitance). The sneak paths on these non-selectedwordlines can exist but may have only small impact on sensing margins,so are not depicted.

With a non-linear memory cell having I-V response depicted by FIG. 5utilized for non-selected cells 908 and selected cell 906, theapproximately 1.5 volts on bitlines 902A, 902C and wordlines 904A, 904Cwill be less than the threshold voltage of the selector components ofthe memory cells (which according to FIG. 5 is above 1.5 volts).Accordingly, the magnitude of sneak path currents in array 900 will bequite small, having negligible effect on sensing margin for selectedcell 908, despite the fact that memory components 918 of non-selectedcells 908 are in an “on” memory state. This is because selectorcomponents 916 of non-selected cells 908 are in a non-conducting state,reducing current through non-selected cells 906 by about four orders ofmagnitude, despite the fact that memory components 918 of non-selectedcells 908 are programmed to a relatively conducting state. In otherembodiments, inter-bitline and inter-wordline capacitive couplingeffects can be reduced even further (e.g., by utilizing relatively smalllocal wordlines or local bitlines having small capacitance for array900). Where capacitive coupling effects are reduced (or where programvoltage can be reduced) so that floating bitlines 902A, 902C or floatingwordlines 904A, 904C have less than about 200 millivolts of voltageeach, then a non-linear memory cell having the I-V response of FIG. 6can be utilized for array 900. In this case, magnitude of sneak pathcurrents can be reduced even more by the respective selector components916 (e.g., up to about seven orders of magnitude). This large reductionin current can enable quite large numbers, n, of memory cells in a 1T-nRarray architecture, while maintaining acceptable sensing margin forselected cell 908. Accordingly, such a 1T-nR architecture can providevery good memory density even for advanced technology nodes (e.g., 22 nmor less).

The aforementioned diagrams have been described with respect tointeraction between several components (e.g., layers) of a memory cell,a conductive layer thereof, or a memory architecture comprised of suchmemory cell/conductive layer. It should be appreciated that in somesuitable alternative aspects of the subject disclosure, such diagramscan include those components and layers specified therein, some of thespecified components/layers, or additional components/layers.Sub-components can also be implemented as electrically connected toother sub-components rather than included within a parentcomponent/layer. For example, an intermediary layer(s) can be institutedadjacent to one or more of the disclosed layers. As one example, asuitable barrier layer that mitigates or controls unintended oxidationcan be positioned between one or more disclosed layers. In yet otherembodiments, a disclosed memory stack or set of film layers can havefewer layers than depicted. For instance, a switching layer canelectrically contact a conductive wire directly, rather than having anelectrode layer there between. Additionally, it is noted that one ormore disclosed processes can be combined into a single process providingaggregate functionality. Components of the disclosed architectures canalso interact with one or more other components not specificallydescribed herein but known by those of skill in the art.

In view of the exemplary diagrams described supra, process methods thatcan be implemented in accordance with the disclosed subject matter willbe better appreciated with reference to the flow charts of FIGS. 10-12.While for purposes of simplicity of explanation, the methods of FIGS.10-12 are shown and described as a series of blocks, it is to beunderstood and appreciated that the claimed subject matter is notlimited by the order of the blocks, as some blocks may occur indifferent orders or concurrently with other blocks from what is depictedand described herein. Moreover, not all illustrated blocks arenecessarily required to implement the methods described herein.Additionally, it should be further appreciated that some or all of themethods disclosed throughout this specification are capable of beingstored on an article of manufacture to facilitate transporting andtransferring such methodologies to an electronic device. The termarticle of manufacture, as used, is intended to encompass a computerprogram accessible from any computer-readable device, device inconjunction with a carrier, or storage medium.

FIG. 10 illustrates a flowchart of an example method 1000 forfabricating a solid state selector device. At 1002, method 1000 cancomprise providing a first layer structure comprising a first metalmaterial. At 1004, method 1000 can comprise providing a layer ofselector material adjacent to the first layer structure. In at least oneembodiment, the layer of selector material can be in contact with thefirst layer structure. At 1006, method 1000 can comprise providing asecond layer structure comprising a second metal material adjacent tothe layer of the selector material. In at least one embodiment, thesecond layer structure can be in contact with the layer of the selectormaterial. In alternative or additional embodiments, the first metalmaterial can be configured to provide conductive ions to the selectormaterial in response to a voltage applied across the first layerstructure and the second layer structure. In other embodiments, theselector material can be configured to allow the conductive ions topermeate within the layer of selector material in response to thevoltage applied across the first layer structure and the second layerstructure. According to still other embodiments, the first layerstructure, the layer of selector material, and the second layerstructure can form the solid state selector device. In still furtherembodiments, the selector device can be disposed in electrical serieswith a two-terminal memory device.

According to another embodiment(s), the second metal material can beconfigured to provide further conductive ions to the selector materialin response to a second voltage, of different polarity (e.g., oppositepolarity) as the voltage, applied across the first layer structure andthe second layer structure. In at least one embodiment, the furtherconductive ions can at least in part dissipate from the layer of theselector material in response to a magnitude of the voltage or thesecond voltage falling below a threshold voltage magnitude. In a furtherembodiment(s), conductivity of the layer of selector material can bedecreased in response to the further conductive ions at least in partdissipating from the layer of the selector material.

In still other embodiments, the first metal material can be selectedfrom a group consisting of: a noble metal (e.g. Pt, Pd, Ag, Au), a metalalloy containing a noble metal in part, a fast electric field enhanceddiffuser (e.g. Ni, Cu, Ag, Co, Fe) and a CMOS wiring metal (e.g. W, Al,Ti, TiN, TaN, WN). In another embodiment, the layer of the selectormaterial can be selected from a group consisting of: an insulator, anon-stoichiometric oxide, a chalcogenide, a solid-electrolyte containingone or more of Ge, Sb, S and Te, and a metal-doped material. In yetanother embodiment, providing the first layer structure can furthercomprise providing a first electrode comprising a metal material that isselected from a group consisting of: an active metal, W, Al, Cu, TiN andTiW. In still another embodiment(s), providing the first layer structurecan additionally comprise providing a first ion conductor disposedbetween the layer of selector material and the metal material that isselected from a second group consisting of: an ion conductor, anelectrolyte, a metal oxide, and a metal oxide alloy.

According to further embodiments, method 1000 can additionally compriseforming a plurality of two-terminal memory devices upon a semiconductorsubstrate, and forming a plurality of selector devices. In one or moreembodiments, each of the two-terminal memory devices can be associatedwith at least one selector device from the plurality of selectordevices. In another embodiment(s), the plurality of two-terminal memorydevices can comprise the two-terminal memory device and the plurality ofselector devices can comprise the selector device. In other embodiments,the method can additionally comprise forming a crossbar memory structurefrom the plurality of two-terminal memory devices and the plurality ofselector devices.

FIG. 11 illustrates a flowchart of an example method 1100 forfabricating a two-terminal memory having a non-linear I-Vcharacteristic, according to additional embodiments of the presentdisclosure. At 1102, method 1100 can comprise forming a first layerstructure comprising a first metal material on a substrate. In at leastone embodiment, the substrate can comprise one or more electronicdevices (e.g., CMOS devices, SOI devices, and so on) formed therein orthereon. At 1104, method 1100 can comprise forming an ion conductorlayer in contact with the first layer structure. Additionally, at 1106,method 1100 can comprise forming a layer of selector material in contactwith the ion conductor layer. At 1108, method 1100 can comprise forminga second ion conductor layer in contact with the selector material.Further, at 1110, method 1100 can comprise forming a second layerstructure comprising a metal material and in contact with the second ionconductor. In addition to the foregoing, at 1112, method 1100 cancomprise forming a two-terminal memory device in electrical series withthe second layer structure. At 1114, method 1100 can comprise connectinga first conductor of a memory device to the first layer structure. At1116, method 1100 can comprise connecting a second conductor of thememory device to the two-terminal memory device.

FIG. 12 illustrates a flowchart of an example method 1200 for operatinga crossbar memory array according to further embodiments of the subjectdisclosure. For instance, the crossbar memory array can comprise aplurality of two-terminal memory devices and a plurality of selectordevices, wherein each of the plurality of two-terminal memory devicescan be associated in series with one selector device from the pluralityof selector devices, wherein each selector device is associated with afirst electrical characteristic in response to an applied voltage lessthan a threshold voltage, and can be associated with a second electricalcharacteristic in response to an applied voltage greater or equal to thethreshold voltage. At 1202, method 1200 can comprise applying a firstvoltage greater than the threshold voltage to a first memory structurecomprising a first two-terminal memory device in series with a firstselector device. At 1204, method 1200 can comprise applying a secondvoltage, concurrently with applying the first voltage, that is less thanthe threshold voltage to a second memory structure comprising a secondtwo-terminal memory device in series with a second selector device. At1206, method 1200 can comprise determining a current in response toapplying the first voltage concurrent with applying the second voltage.In various embodiments, the current comprises a first current associatedwith the first selector device and a second current associated with thesecond selector device. Further, a current ratio of the first current tothe second current can be within a range of ratios selected from a groupof ranges consisting of: about 1,000 to about 10,000, about 10,000 toabout 100,000, about 100,000 to about 1,000,000, and about 1,000,000 toabout 10,000,000. In further embodiments, the first two-terminal memorydevice and the second two-terminal memory device can both be in aprogrammed state.

According to one or more additional embodiments, a selector device ofthe plurality of selector devices can comprise a first active metallayer, a second active metal layer, and a selection layer disposedbetween the first active metal layer and the second active metal layer.In another embodiment(s), applying the second voltage concurrently withapplying the first voltage can further comprise applying the firstvoltage greater than the threshold voltage to the first selector deviceto thereby cause a conductive filament of metallic ion particles of afirst active metal layer to be formed within the selection layer of thefirst selector device, and applying the second voltage less than thethreshold voltage to the second selector device, wherein a conductivefilament of metallic ion particles of a first active metal layer is notformed within a selection layer of the second selector device (or isformed only within a subset of the selection layer of the secondselector device, and does not provide a conductive path(s) through theselection layer of the second selector device).

According to further embodiments, the threshold voltage can be within arange selected from a group of ranges consisting of: about 0.1 volt toabout 2 volts, and about 2 volts to about 4 volts. In anotherembodiment(s), the second current can be selected from a range of about1×10⁻⁸ amps to about 1×10⁻¹⁴ amps. In still other embodiments, the firstcurrent can be selected from a range of about 1×10⁻³ amps to about1×10⁻⁶ amps.

In additional embodiments, applying the second voltage concurrently withapplying the first voltage can further comprise applying the secondvoltage less than the threshold voltage to a second plurality oftwo-terminal memory devices, different from the plurality oftwo-terminal memory devices, in series with a second plurality ofselector devices, different from the plurality of selector devices. Inanother embodiment, a number of two-terminal memory devices in thesecond plurality of two-terminal memory devices can be selected from arange of about 1,000 to about 250,000. In still other embodiments, thefirst two-terminal memory device and the second two-terminal memorydevice are both in an erased state. In yet another embodiment(s), thetwo-terminal memory device comprises a filamentary-based resistivememory device.

In various embodiments of the subject disclosure, disclosed memory ormemory architectures can be employed as a standalone or integratedembedded memory device with a CPU or microcomputer. Some embodiments canbe implemented, for instance, as part of a computer memory (e.g., randomaccess memory, cache memory, read-only memory, storage memory, or thelike). Other embodiments can be implemented, for instance, as a portablememory device. Examples of suitable portable memory devices can includeremovable memory, such as a secure digital (SD) card, a universal serialbus (USB) memory stick, a compact flash (CF) card, or the like, orsuitable combinations of the foregoing. (See, e.g., FIGS. 13 and 14,infra).

NAND FLASH is employed for compact FLASH devices, USB devices, SD cards,solid state drives (SSDs), and storage class memory, as well as otherform-factors. Although NAND has proven a successful technology infueling the drive to scale down to smaller devices and higher chipdensities over the past decade, as technology scaled down past 25nanometer (nm) memory cell technology, several structural, performance,and reliability problems became evident. A subset of these or similarconsiderations are addressed by the disclosed aspects.

In order to provide a context for the various aspects of the disclosedsubject matter, FIG. 13, as well as the following discussion, isintended to provide a brief, general description of a suitableenvironment in which various aspects of the disclosed subject matter canbe implemented or processed. While the subject matter has been describedabove in the general context of solid state memory and semiconductorarchitectures and process methodologies for fabricating and operatingsuch memory or architectures, those skilled in the art will recognizethat the subject disclosure also can be implemented in combination withother architectures or process methodologies. Moreover, those skilled inthe art will appreciate that the disclosed processes can be practicedwith a processing system or a computer processor, either alone or inconjunction with a host computer (e.g., computer 1402 of FIG. 14,infra), which can include single-processor or multiprocessor computersystems, mini-computing devices, mainframe computers, as well aspersonal computers, hand-held computing devices (e.g., PDA, smart phone,watch), microprocessor-based or programmable consumer or industrialelectronics, and the like. The illustrated aspects may also be practicedin distributed computing environments where tasks are performed byremote processing devices that are linked through a communicationsnetwork. However, some, if not all aspects of the subject innovation canbe practiced on stand-alone electronic devices, such as a memory card,Flash memory module, removable memory, or the like. In a distributedcomputing environment, program modules can be located in both local andremote memory storage modules or devices.

FIG. 13 illustrates a block diagram of an example operating and controlenvironment 1300 for a memory cell array 1302 according to aspects ofthe subject disclosure. In at least one aspect of the subjectdisclosure, memory cell array 1302 can comprise a variety of memory celltechnology. In at least one embodiment, memory cells of the memory celltechnology can comprise two-terminal memory having a non-linear I-Vresponse(s), as described herein. In another embodiment, memory cellarray 1302 can store operations configured to cause a device tofabricate a two-terminal memory cell electrically in series with aselector device.

A column controller 1306 can be formed adjacent to memory cell array1302. Moreover, column controller 1306 can be electrically coupled withbit lines of memory cell array 1302. Column controller 1306 can controlrespective bitlines, applying suitable program, erase or read voltagesto selected bitlines.

In addition, operating and control environment 1300 can comprise a rowcontroller 1304. Row controller 1304 can be formed adjacent to columncontroller 1306, and electrically connected with word lines of memorycell array 1302. Row controller 1304 can select particular rows ofmemory cells with a suitable selection voltage. Moreover, row controller1304 can facilitate program, erase or read operations by applyingsuitable voltages at selected word lines.

A clock source(s) 1308 can provide respective clock pulses to facilitatetiming for read, write, and program operations of row controller 1304and column controller 1306. Clock source(s) 1308 can further facilitateselection of word lines or bit lines in response to external or internalcommands received by operating and control environment 1300. Aninput/output buffer 1312 can be connected to an external host apparatus,such as a computer or other processing device (not depicted, but seee.g., computer 802 of FIG. 12, infra) by way of an I/O buffer or otherI/O communication interface. Input/output buffer 1312 can be configuredto receive write data, receive an erase instruction, output readoutdata, and receive address data and command data, as well as address datafor respective instructions. Address data can be transferred to rowcontroller 1304 and column controller 1306 by an address register 1310.In addition, input data is transmitted to memory cell array 1302 viasignal input lines, and output data is received from memory cell array1302 via signal output lines. Input data can be received from the hostapparatus, and output data can be delivered to the host apparatus viathe I/O buffer.

Commands received from the host apparatus can be provided to a commandinterface 1314. Command interface 1314 can be configured to receiveexternal control signals from the host apparatus, and determine whetherdata input to the input/output buffer 1312 is write data, a command, oran address. Input commands can be transferred to a state machine 1316.

State machine 1316 can be configured to manage programming andreprogramming of memory cell array 1302. State machine 1316 receivescommands from the host apparatus via input/output buffer 1312 andcommand interface 1314, and manages read, write, erase, data input, dataoutput, and similar functionality associated with memory cell array1302. In some aspects, state machine 1316 can send and receiveacknowledgments and negative acknowledgments regarding successfulreceipt or execution of various commands.

To implement read, write, erase, input, output, etc., functionality,state machine 1316 can control clock source(s) 1308. Control of clocksource(s) 1308 can cause output pulses configured to facilitate rowcontroller 1304 and column controller 1306 implementing the particularfunctionality. Output pulses can be transferred to selected bit lines bycolumn controller 1306, for instance, or word lines by row controller1304, for instance.

In connection with FIG. 14, the systems and processes described belowcan be embodied within hardware, such as a single integrated circuit(IC) chip, multiple ICs, an application specific integrated circuit(ASIC), or the like. Further, the order in which some or all of theprocess blocks appear in each process should not be deemed limiting.Rather, it should be understood that some of the process blocks can beexecuted in a variety of orders, not all of which may be explicitlyillustrated herein.

With reference to FIG. 14, a suitable operating environment 1400 forimplementing various aspects of the claimed subject matter includes acomputer 1402. The computer 1402 includes a processing unit 1404, asystem memory 1406, a codec 1435, and a system bus 1408. The system bus1408 couples system components including, but not limited to, the systemmemory 1406 to the processing unit 1404. The processing unit 1404 can beany of various available processors. Dual microprocessors and othermultiprocessor architectures also can be employed as the processing unit1404.

The system bus 1408 can be any of several types of bus structure(s)including the memory bus or memory controller, a peripheral bus orexternal bus, and/or a local bus using any variety of available busarchitectures including, but not limited to, Industrial StandardArchitecture (ISA), Micro-Channel Architecture (MSA), Extended ISA(EISA), Intelligent Drive Electronics (IDE), VESA Local Bus (VLB),Peripheral Component Interconnect (PCI), Card Bus, Universal Serial Bus(USB), Advanced Graphics Port (AGP), Personal Computer Memory CardInternational Association bus (PCMCIA), Firewire (IEEE 1394), and SmallComputer Systems Interface (SCSI).

The system memory 1406 includes volatile memory 1410 and non-volatilememory 1414, which can employ one or more of the disclosed memoryarchitectures, in various embodiments. The basic input/output system(BIOS), containing the basic routines to transfer information betweenelements within the computer 1402, such as during start-up, is stored innon-volatile memory 1412. In addition, according to present innovations,codec 1435 may include at least one of an encoder or decoder, whereinthe at least one of an encoder or decoder may consist of hardware,software, or a combination of hardware and software. Although, codec1435 is depicted as a separate component, codec 1435 may be containedwithin non-volatile memory 1412. By way of illustration, and notlimitation, non-volatile memory 1412 can include read only memory (ROM),programmable ROM (PROM), electrically programmable ROM (EPROM),electrically erasable programmable ROM (EEPROM), or Flash memory.Non-volatile memory 1412 can employ one or more of the disclosed memoryarchitectures, in at least some disclosed embodiments. Moreover,non-volatile memory 1412 can be computer memory (e.g., physicallyintegrated with computer 1402 or a mainboard thereof), or removablememory. Examples of suitable removable memory with which disclosedembodiments can be implemented can include a secure digital (SD) card, acompact Flash (CF) card, a universal serial bus (USB) memory stick, orthe like. Volatile memory 1410 includes random access memory (RAM),which acts as external cache memory, and can also employ one or moredisclosed memory architectures in various embodiments. By way ofillustration and not limitation, RAM is available in many forms such asstatic RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), doubledata rate SDRAM (DDR SDRAM), and enhanced SDRAM (ESDRAM), and so forth.

Computer 1402 may also include removable/non-removable,volatile/non-volatile computer storage medium. FIG. 14 illustrates, forexample, disk storage 1414. Disk storage 1414 includes, but is notlimited to, devices such as a magnetic disk drive, solid state disk(SSD) floppy disk drive, tape drive, Jaz drive, Zip drive, LS-100 drive,flash memory card, or memory stick. In addition, disk storage 1414 caninclude storage medium separately or in combination with other storagemedium including, but not limited to, an optical disk drive such as acompact disk ROM device (CD-ROM), CD recordable drive (CD-R Drive), CDrewritable drive (CD-RW Drive) or a digital versatile disk ROM drive(DVD-ROM). To facilitate connection of the disk storage 1414 to thesystem bus 1408, a removable or non-removable interface is typicallyused, such as interface 1416. It is appreciated that disk storage 1414can store information related to a user. Such information might bestored at or provided to a server or to an application running on a userdevice. In one embodiment, the user can be notified (e.g., by way ofoutput device(s) 1436) of the types of information that are stored todisk storage 1414 and/or transmitted to the server or application. Theuser can be provided the opportunity to opt-in or opt-out of having suchinformation collected and/or shared with the server or application(e.g., by way of input from input device(s) 1428).

It is to be appreciated that FIG. 14 describes software that acts as anintermediary between users and the basic computer resources described inthe suitable operating environment 1400. Such software includes anoperating system 1418. Operating system 1418, which can be stored ondisk storage 1414, acts to control and allocate resources of thecomputer 1402. Applications 1420 take advantage of the management ofresources by operating system 1418 through program modules 1424, andprogram data 1426, such as the boot/shutdown transaction table and thelike, stored either in system memory 1406 or on disk storage 1414. It isto be appreciated that the claimed subject matter can be implementedwith various operating systems or combinations of operating systems.

A user enters commands or information into the computer 1402 throughinput device(s) 1428. Input devices 1428 include, but are not limitedto, a pointing device such as a mouse, trackball, stylus, touch pad,keyboard, microphone, joystick, game pad, satellite dish, scanner, TVtuner card, digital camera, digital video camera, web camera, and thelike. These and other input devices connect to the processing unit 1404through the system bus 1408 via interface port(s) 1430. Interfaceport(s) 1430 include, for example, a serial port, a parallel port, agame port, and a universal serial bus (USB). Output device(s) 1436 usesome of the same type of ports as input device(s) 1428. Thus, forexample, a USB port may be used to provide input to computer 1402 and tooutput information from computer 1402 to an output device 1436. Outputadapter 1434 is provided to illustrate that there are some outputdevices, such as monitors, speakers, and printers, among other outputdevices, which require special adapters. The output adapter 1434 caninclude, by way of illustration and not limitation, video and soundcards that provide a means of connection between the output device 1436and the system bus 1408. It should be noted that other devices and/orsystems of devices provide both input and output capabilities such asremote computer(s) 1438.

Computer 1402 can operate in a networked environment using logicalconnections to one or more remote computers, such as remote computer(s)1438. The remote computer(s) 1438 can be a personal computer, a server,a router, a network PC, a workstation, a microprocessor based appliance,a peer device, a smart phone, a tablet, or other network node, andtypically includes many of the elements described relative to computer1402. For purposes of brevity, only a memory storage device 1440 isillustrated with remote computer(s) 1438. Remote computer(s) 1438 islogically connected to computer 1402 through a network interface 1442and then connected via communication connection(s) 1444. Networkinterface 1442 encompasses wire and/or wireless communication networkssuch as local-area networks (LAN) and wide-area networks (WAN) andcellular networks. LAN technologies include Fiber Distributed DataInterface (FDDI), Copper Distributed Data Interface (CDDI), Ethernet,Token Ring and the like. WAN technologies include, but are not limitedto, point-to-point links, circuit switching networks such as IntegratedServices Digital Networks (ISDN) and variations thereon, packetswitching networks, and Digital Subscriber Lines (DSL).

Communication connection(s) 1444 refers to the hardware/softwareemployed to connect the network interface 1442 to the system bus 1408.While communication connection 1444 is shown for illustrative clarityinside computer 1402, it can also be external to computer 1402. Thehardware/software necessary for connection to the network interface 1442includes, for exemplary purposes only, internal and externaltechnologies such as, modems including regular telephone grade modems,cable modems and DSL modems, ISDN adapters, and wired and wirelessEthernet cards, hubs, and routers.

The illustrated aspects of the disclosure may also be practiced indistributed computing environments where certain tasks are performed byremote processing devices that are linked through a communicationsnetwork. In a distributed computing environment, program modules orstored information, instructions, or the like can be located in local orremote memory storage devices.

Moreover, it is to be appreciated that various components describedherein can include electrical circuit(s) that can include components andcircuitry elements of suitable value in order to implement theembodiments of the subject disclosure. Furthermore, it can beappreciated that many of the various components can be implemented onone or more IC chips. For example, in one embodiment, a set ofcomponents can be implemented in a single IC chip. In other embodiments,one or more of respective components are fabricated or implemented onseparate IC chips.

As utilized herein, terms “component,” “system,” “architecture” and thelike are intended to refer to a computer or electronic-related entity,either hardware, a combination of hardware and software, software (e.g.,in execution), or firmware. For example, a component can be one or moretransistors, a memory cell, an arrangement of transistors or memorycells, a gate array, a programmable gate array, an application specificintegrated circuit, a controller, a processor, a process running on theprocessor, an object, executable, program or application accessing orinterfacing with semiconductor memory, a computer, or the like, or asuitable combination thereof. The component can include erasableprogramming (e.g., process instructions at least in part stored inerasable memory) or hard programming (e.g., process instructions burnedinto non-erasable memory at manufacture).

By way of illustration, both a process executed from memory and theprocessor can be a component. As another example, an architecture caninclude an arrangement of electronic hardware (e.g., parallel or serialtransistors), processing instructions and a processor, which implementthe processing instructions in a manner suitable to the arrangement ofelectronic hardware. In addition, an architecture can include a singlecomponent (e.g., a transistor, a gate array, . . . ) or an arrangementof components (e.g., a series or parallel arrangement of transistors, agate array connected with program circuitry, power leads, electricalground, input signal lines and output signal lines, and so on). A systemcan include one or more components as well as one or more architectures.One example system can include a switching block architecture comprisingcrossed input/output lines and pass gate transistors, as well as powersource(s), signal generator(s), communication bus(ses), controllers, I/Ointerface, address registers, and so on. It is to be appreciated thatsome overlap in definitions is anticipated, and an architecture or asystem can be a stand-alone component, or a component of anotherarchitecture, system, etc.

In addition to the foregoing, the disclosed subject matter can beimplemented as a method, apparatus, or article of manufacture usingtypical manufacturing, programming or engineering techniques to producehardware, firmware, software, or any suitable combination thereof tocontrol an electronic device to implement the disclosed subject matter.The terms “apparatus” and “article of manufacture” where used herein areintended to encompass an electronic device, a semiconductor device, acomputer, or a computer program accessible from any computer-readabledevice, carrier, or media. Computer-readable media can include hardwaremedia, or software media. In addition, the media can includenon-transitory media, or transport media. In one example, non-transitorymedia can include computer readable hardware media. Specific examples ofcomputer readable hardware media can include but are not limited tomagnetic storage devices (e.g., hard disk, floppy disk, magnetic strips. . . ), optical disks (e.g., compact disk (CD), digital versatile disk(DVD) . . . ), smart cards, and flash memory devices (e.g., card, stick,key drive . . . ). Computer-readable transport media can include carrierwaves, or the like. Of course, those skilled in the art will recognizemany modifications can be made to this configuration without departingfrom the scope or spirit of the disclosed subject matter.

What has been described above includes examples of the subjectinnovation. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe subject innovation, but one of ordinary skill in the art canrecognize that many further combinations and permutations of the subjectinnovation are possible. Accordingly, the disclosed subject matter isintended to embrace all such alterations, modifications and variationsthat fall within the spirit and scope of the disclosure. Furthermore, tothe extent that a term “includes”, “including”, “has” or “having” andvariants thereof is used in either the detailed description or theclaims, such term is intended to be inclusive in a manner similar to theterm “comprising” as “comprising” is interpreted when employed as atransitional word in a claim.

Moreover, the word “exemplary” is used herein to mean serving as anexample, instance, or illustration. Any aspect or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Rather, use of the wordexemplary is intended to present concepts in a concrete fashion. As usedin this application, the term “or” is intended to mean an inclusive “or”rather than an exclusive “or”. That is, unless specified otherwise, orclear from context, “X employs A or B” is intended to mean any of thenatural inclusive permutations. That is, if X employs A; X employs B; orX employs both A and B, then “X employs A or B” is satisfied under anyof the foregoing instances. In addition, the articles “a” and “an” asused in this application and the appended claims should generally beconstrued to mean “one or more” unless specified otherwise or clear fromcontext to be directed to a singular form.

Additionally, some portions of the detailed description have beenpresented in terms of algorithms or process operations on data bitswithin electronic memory. These process descriptions or representationsare mechanisms employed by those cognizant in the art to effectivelyconvey the substance of their work to others equally skilled. A processis here, generally, conceived to be a self-consistent sequence of actsleading to a desired result. The acts are those requiring physicalmanipulations of physical quantities. Typically, though not necessarily,these quantities take the form of electrical and/or magnetic signalscapable of being stored, transferred, combined, compared, and/orotherwise manipulated.

It has proven convenient, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like. It should be borne in mind, however, thatall of these and similar terms are to be associated with the appropriatephysical quantities and are merely convenient labels applied to thesequantities. Unless specifically stated otherwise or apparent from theforegoing discussion, it is appreciated that throughout the disclosedsubject matter, discussions utilizing terms such as processing,computing, replicating, mimicking, determining, or transmitting, and thelike, refer to the action and processes of processing systems, and/orsimilar consumer or industrial electronic devices or machines, thatmanipulate or transform data or signals represented as physical(electrical or electronic) quantities within the circuits, registers ormemories of the electronic device(s), into other data or signalssimilarly represented as physical quantities within the machine orcomputer system memories or registers or other such information storage,transmission and/or display devices.

In regard to the various functions performed by the above describedcomponents, architectures, circuits, processes and the like, the terms(including a reference to a “means”) used to describe such componentsare intended to correspond, unless otherwise indicated, to any componentwhich performs the specified function of the described component (e.g.,a functional equivalent), even though not structurally equivalent to thedisclosed structure, which performs the function in the hereinillustrated exemplary aspects of the embodiments. In addition, while aparticular feature may have been disclosed with respect to only one ofseveral implementations, such feature may be combined with one or moreother features of the other implementations as may be desired andadvantageous for any given or particular application. It will also berecognized that the embodiments include a system as well as acomputer-readable medium having computer-executable instructions forperforming the acts and/or events of the various processes.

What is claimed is:
 1. A method for forming a selector device for atwo-terminal memory device, comprising: providing a first layerstructure comprising a first metal material; providing a layer ofselector material in contact with the first layer structure; andproviding a second layer structure comprising a second metal materialand in contact with the layer of the selector material, wherein: thefirst metal material is configured to provide conductive ions to theselector material in response to a voltage applied across the firstlayer structure and the second layer structure, the selector material isconfigured to allow the conductive ions to permeate within the layer ofselector material and form a conductive filament across the selectormaterial in response to the voltage applied across the first layerstructure and the second layer structure, wherein the selector materialis configured to facilitate a break in electrical continuity of theconductive filament in response to a reduction in magnitude of thevoltage to a reduced voltage, greater than zero, and having a samepolarity as the voltage, the first layer structure, the layer ofselector material, and the second layer structure form the selectordevice, and the selector device is disposed in electrical series withthe two-terminal memory device.
 2. The method of claim 1, wherein thesecond metal material is configured to provide further conductive ionsto the selector material in response to a second voltage, of oppositepolarity as the voltage, applied across the first layer structure andthe second layer structure.
 3. The method of claim 2, wherein: thefurther conductive ions at least in part dissipate from the layer ofselector material in response to a reduction in magnitude of the secondvoltage to a second reduced voltage, greater than zero magnitude; andconductivity of the layer of selector material is decreased in responseto the further conductive ions at least in part dissipating from thelayer of the selector material.
 4. The method of claim 3, wherein themagnitude of the voltage is substantially the same as a second magnitudeof the second voltage.
 5. The method of claim 4, wherein providing thefirst layer structure and providing the second layer structure furthercomprise selecting a material comprising a common metal for the firstmetal material and for the second metal material.
 6. The method of claim3, wherein the magnitude of the voltage is different in magnitude from asecond magnitude of the second voltage.
 7. The method of claim 6,wherein providing the first layer structure and providing the secondlayer structure further comprising employing different metals for thefirst metal material and for the second metal material.
 8. The method ofclaim 1, wherein at least one of: the first metal material or the secondmetal material is selected from a group consisting of: a noble metal, ametal alloy at least in part comprising a noble metal, a fast electricfield enhanced diffuser material, Ni, Cu, Ag, Co, Fe, W, Al, Ti, TiN,TaN, WN, and an alloy of one or more of the foregoing; or the layer ofthe selector material is selected from a group consisting of: aninsulator, a non-stoichiometric oxide, a chalcogenide, asolid-electrolyte comprising Ge, Sb, S and Te, and a metal-dopedmaterial.
 9. The method of claim 1 wherein the providing the first layerstructure or the second layer structure further comprises: providing afirst electrode or a second electrode, respectively, comprising thefirst metal material or the second metal material, respectively, that isselected from a group consisting of: Co, Ni, Fe, Ag, Ti, W, Al, Cu, TiN,TaN, TiW, and an alloy of one or more of the foregoing; and at least oneof: providing a first ion conductor disposed between the layer ofselector material and the first electrode that is selected from a secondgroup consisting of: an ion conductor, a solid-electrolyte, a metaloxide, and a metal oxide alloy; or providing a second ion conductordisposed between the layer of selector material and the second electrodethat is selected from the second group.
 10. The method of claim 1,further comprising: forming a plurality of two-terminal memory devicesupon a semiconductor substrate; and forming a plurality of selectordevices, wherein: each of the two-terminal memory devices are associatedwith at least one selector device from the plurality of selectordevices, the plurality of two-terminal memory devices comprises thetwo-terminal memory device, and the plurality of selector devicescomprises the selector device.
 11. The method of claim 10, furthercomprising forming a crossbar memory structure from the plurality oftwo-terminal memory devices and the plurality of selector devices. 12.The method of claim 1, wherein providing the layer of selector materialfurther comprises forming the layer of selector material to have fewdefect sites per volume of selector material suitable to trap theconductive ions.
 13. A selector device for a two-terminal memory,comprising: a first layer structure comprising a first metal material; alayer of selector material in contact with the first layer structure;and a second layer structure in contact with the layer of the selectormaterial and comprising a second metal material, wherein: the firstmetal material is configured to provide conductive ions to the selectormaterial in response to a threshold voltage applied across the firstlayer structure and the second layer structure, the second layerstructure is configured to provide additional conductive ions to theselector material in response to a second voltage, having differentpolarity from the threshold voltage, applied across the first layerstructure and the second layer structure, the selector material isconfigured to allow the conductive ions to permeate within the layer ofselector material in response to the threshold voltage applied acrossthe first layer structure and the second layer structure and isconfigured to allow the additional conductive ions to permeate withinthe layer of selector material on response to a second voltage, ofdifferent polarity from the threshold voltage, applied across the firstlayer structure and the second layer structure, and the selector deviceis disposed in electrical series with the two-terminal memory device.14. The selector device of claim 13, wherein: the selector materialconducts a first current in response to an applied voltage less than thethreshold voltage; the conductive ions within the selector materialfacilitate conduction of a second current in response to the appliedvoltage being greater or equal to the threshold voltage; and a ratio ofthe second current to the first current is about 1,000 or greater. 15.The selector device of claim 14, wherein the selector device changesfrom conducting the first current to conducting the second current inresponse to the applied voltage, having been greater or equal to thethreshold voltage, falling to a positive voltage less than the thresholdvoltage.
 16. The selector device of claim 13, wherein: the additionalconductive ions permeate within the selector material to form aconductive sub-region thereof, in response to the second voltage; thelayer of selector material is associated with an increased current inresponse to permeation of the additional conductive ions within theselector material; the additional conductive ions at least in partdeform the conductive sub-region of the layer of selector material inresponse to a magnitude of the second voltage falling below a secondmagnitude threshold; the layer of selector material is associated with adecreased current in response to the additional ions at least in partdeforming the conductive sub-region; and a ratio of the decreasedcurrent to the increased current is 1,000 or greater.
 17. The selectordevice of claim 13, wherein the threshold voltage is selected from arange of about 0.1 volts to about 4 volts and an electrical response ofthe selector device is between at least one of the following ranges:from about 1 milliVolt (mV)/decade to about 60 mV/decade; or from about0.15 decades/mV to about 1 decade/mV.
 18. The selector device of claim13, wherein the selector material has a thickness selected from a rangeof about 0.5 nm to about 50 nm.
 19. The selector device of claim 13,wherein at least one of: the first metal material is selected from agroup consisting of: a noble metal, a metal alloy at least in partcomprising a noble metal, a fast electric field enhanced diffusermaterial, Ni, Cu, Ag, Co, Fe, W, Al, Ti, TiN, TaN, WN and a suitablealloy of the foregoing; or the layer of selector material is selectedfrom a group consisting of: an insulator, a non-stoichiometric oxide, achalcogenide, a solid-electrolyte comprising Ge, Sb, S, or Te, and ametal-doped material.
 20. The selector device of claim 13, wherein thefirst layer structure or the second layer structure comprises: a firstelectrode; and a first ion conductor disposed between the layer ofselector material and the first electrode.